<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2020 Workiva-->
<!--r:e3e9e980-cf57-4e5b-a05b-ba375b8b8481,g:5f849f07-7d4e-418e-b2fe-4e3cfed7128a-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.swgas.com/role/Cover" xlink:type="simple" xlink:href="swx-20200630.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/Cover" xlink:type="extended" id="i5dc6605b1e0e4299b0acf8f9484e99e7_Cover">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_3e9acfb6-5c3a-4271-8c9a-d1a495e29c97" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_DocumentType_3e9acfb6-5c3a-4271-8c9a-d1a495e29c97" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_6cee0ff8-b715-4950-b03e-fa206c78d64f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_DocumentQuarterlyReport_6cee0ff8-b715-4950-b03e-fa206c78d64f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_296aca3c-fcc1-4c73-a205-5bce3f34306f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_DocumentPeriodEndDate_296aca3c-fcc1-4c73-a205-5bce3f34306f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_7f595835-a032-4c12-98e2-c062e1ea0cc4" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_DocumentTransitionReport_7f595835-a032-4c12-98e2-c062e1ea0cc4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_85abf4ef-1890-4d75-8d05-652b032f9a2b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityFileNumber_85abf4ef-1890-4d75-8d05-652b032f9a2b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_56d243f9-345e-447a-9f90-7266fdd2358f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityRegistrantName_56d243f9-345e-447a-9f90-7266fdd2358f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_298acbef-9946-4771-9fd2-074bffc00f4e" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityIncorporationStateCountryCode_298acbef-9946-4771-9fd2-074bffc00f4e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_0873c38d-6828-4c50-a09b-d8bbdf26c737" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityTaxIdentificationNumber_0873c38d-6828-4c50-a09b-d8bbdf26c737" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_da6756a2-20c8-4226-9fcf-c3203e9dce7a" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityAddressAddressLine1_da6756a2-20c8-4226-9fcf-c3203e9dce7a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_70279061-773a-460f-a7c2-ca304b0b291d" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityAddressAddressLine2_70279061-773a-460f-a7c2-ca304b0b291d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_2c496dd0-b161-4a4e-9100-87b4c625d30c" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityAddressCityOrTown_2c496dd0-b161-4a4e-9100-87b4c625d30c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_16ba4ab8-90bb-4fb1-9774-5c532f982abf" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityAddressStateOrProvince_16ba4ab8-90bb-4fb1-9774-5c532f982abf" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_f1b72f4e-6d20-49d7-8d8f-543b23df2af3" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityAddressPostalZipCode_f1b72f4e-6d20-49d7-8d8f-543b23df2af3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_f28ecfac-1b10-4e01-babb-8334a5e0396b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_CityAreaCode_f28ecfac-1b10-4e01-babb-8334a5e0396b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_cead61a9-f81f-4202-95a8-65cdfa87454f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_LocalPhoneNumber_cead61a9-f81f-4202-95a8-65cdfa87454f" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_c68cab43-43b8-4936-b7d3-2fe12b4087e9" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_Security12bTitle_c68cab43-43b8-4936-b7d3-2fe12b4087e9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_c7d22112-af9e-4587-9895-f62f0efd2228" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_TradingSymbol_c7d22112-af9e-4587-9895-f62f0efd2228" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_133886f3-c970-491f-86c8-80d60749815b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_SecurityExchangeName_133886f3-c970-491f-86c8-80d60749815b" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_e7069a38-d16b-419c-bec2-a842fc39a5e3" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityCurrentReportingStatus_e7069a38-d16b-419c-bec2-a842fc39a5e3" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_b85ef747-759d-45be-98a7-21be4b2ce920" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityInteractiveDataCurrent_b85ef747-759d-45be-98a7-21be4b2ce920" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_d7f91063-5ebe-4af6-90b1-a37faf9a15b0" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityFilerCategory_d7f91063-5ebe-4af6-90b1-a37faf9a15b0" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_a5044e15-3c5a-44cf-af14-de683c836e2b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntitySmallBusiness_a5044e15-3c5a-44cf-af14-de683c836e2b" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_fd499a30-dd02-4df4-9813-c7485cbbe0ee" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityEmergingGrowthCompany_fd499a30-dd02-4df4-9813-c7485cbbe0ee" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_2e164de9-7d13-4bfd-a8fe-4716a4f34a3a" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityShellCompany_2e164de9-7d13-4bfd-a8fe-4716a4f34a3a" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_efac035b-5022-4de9-942d-e41e412e1470" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_efac035b-5022-4de9-942d-e41e412e1470" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_bd44742d-2c02-4eea-b775-ca5aab79e8ce" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntityCentralIndexKey_bd44742d-2c02-4eea-b775-ca5aab79e8ce" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_0b55ac17-57e3-4186-925a-db881e93e815" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_CurrentFiscalYearEndDate_0b55ac17-57e3-4186-925a-db881e93e815" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_5bed0ea6-df6d-47af-ae32-6192a0cf55c7" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_DocumentFiscalYearFocus_5bed0ea6-df6d-47af-ae32-6192a0cf55c7" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_616671cf-11c5-4ec8-ae4c-8344ca92f454" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_DocumentFiscalPeriodFocus_616671cf-11c5-4ec8-ae4c-8344ca92f454" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_00448c01-0b1b-418f-a908-4c3bc9550eae" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_AmendmentFlag_00448c01-0b1b-418f-a908-4c3bc9550eae" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitiesTable_0324b16f-5c69-42bf-b697-3fd51b993c0d" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityInformationLineItems_03cb47f6-84b2-4c88-9cfa-b13ef322906c" xlink:to="loc_dei_EntitiesTable_0324b16f-5c69-42bf-b697-3fd51b993c0d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_e862f853-5773-4329-a44b-2f3c250adeeb" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntitiesTable_0324b16f-5c69-42bf-b697-3fd51b993c0d" xlink:to="loc_dei_LegalEntityAxis_e862f853-5773-4329-a44b-2f3c250adeeb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e862f853-5773-4329-a44b-2f3c250adeeb_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_e862f853-5773-4329-a44b-2f3c250adeeb" xlink:to="loc_dei_EntityDomain_e862f853-5773-4329-a44b-2f3c250adeeb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a6e00b2c-ba45-4260-af75-dbb4385d6180" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_e862f853-5773-4329-a44b-2f3c250adeeb" xlink:to="loc_dei_EntityDomain_a6e00b2c-ba45-4260-af75-dbb4385d6180" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_985c34d7-7628-4eb6-b9b7-67b20a982fbe" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a6e00b2c-ba45-4260-af75-dbb4385d6180" xlink:to="loc_swx_SouthwestGasCorporationMember_985c34d7-7628-4eb6-b9b7-67b20a982fbe" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="swx-20200630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended" id="id898995e7ae847d89aca7c4b32d05525_CONDENSEDCONSOLIDATEDBALANCESHEETS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_8ed6a0e5-c581-4902-9961-17892e417932" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_d2e5c7a3-0a8e-47d9-b6a6-164c321b23eb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_8ed6a0e5-c581-4902-9961-17892e417932" xlink:to="loc_us-gaap_AssetsAbstract_d2e5c7a3-0a8e-47d9-b6a6-164c321b23eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_c3d151d0-d038-4b96-8cc0-e7d495389a1a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d2e5c7a3-0a8e-47d9-b6a6-164c321b23eb" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_c3d151d0-d038-4b96-8cc0-e7d495389a1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_PublicUtilitiesPropertyPlantandEquipmentGasPlant_86f4de2d-bd2d-46b6-9b82-d550aa38d347" xlink:href="swx-20200630.xsd#swx_PublicUtilitiesPropertyPlantandEquipmentGasPlant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_c3d151d0-d038-4b96-8cc0-e7d495389a1a" xlink:to="loc_swx_PublicUtilitiesPropertyPlantandEquipmentGasPlant_86f4de2d-bd2d-46b6-9b82-d550aa38d347" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation_c5cad59c-0984-47af-8208-ac06b50d7e12" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_c3d151d0-d038-4b96-8cc0-e7d495389a1a" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentAccumulatedDepreciation_c5cad59c-0984-47af-8208-ac06b50d7e12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress_0f83b915-21d6-42c4-8545-ac2938568ff6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_c3d151d0-d038-4b96-8cc0-e7d495389a1a" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentConstructionWorkInProgress_0f83b915-21d6-42c4-8545-ac2938568ff6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_822ba097-bf02-4a1c-8fe1-ba40ea12fe99" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNetAbstract_c3d151d0-d038-4b96-8cc0-e7d495389a1a" xlink:to="loc_us-gaap_PublicUtilitiesPropertyPlantAndEquipmentNet_822ba097-bf02-4a1c-8fe1-ba40ea12fe99" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherPropertyAndInvestments_57dd0e03-41d9-477c-9223-38a849c82690" xlink:href="swx-20200630.xsd#swx_OtherPropertyAndInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d2e5c7a3-0a8e-47d9-b6a6-164c321b23eb" xlink:to="loc_swx_OtherPropertyAndInvestments_57dd0e03-41d9-477c-9223-38a849c82690" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d2e5c7a3-0a8e-47d9-b6a6-164c321b23eb" xlink:to="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_90196812-c5f5-4368-932b-5947e3d2ee33" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_90196812-c5f5-4368-932b-5947e3d2ee33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_6da383cc-2088-4848-b18c-d5ab79f50356" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_6da383cc-2088-4848-b18c-d5ab79f50356" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccruedUtilityRevenue_94e7be72-8f9a-4889-bf8a-e65a8d6ef953" xlink:href="swx-20200630.xsd#swx_AccruedUtilityRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:to="loc_swx_AccruedUtilityRevenue_94e7be72-8f9a-4889-bf8a-e65a8d6ef953" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesReceivable_40bc16e5-f5bb-41cb-b2db-d161af271416" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:to="loc_us-gaap_IncomeTaxesReceivable_40bc16e5-f5bb-41cb-b2db-d161af271416" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredGasCost_f1ca3f98-39da-423e-898d-d902844e0a14" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredGasCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:to="loc_us-gaap_DeferredGasCost_f1ca3f98-39da-423e-898d-d902844e0a14" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_0834955e-d194-4741-a812-432016eecdfc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_0834955e-d194-4741-a812-432016eecdfc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_b45e4ed3-e316-458a-aba1-06af54f58613" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_8423b68b-0afd-445e-9d6a-adb904353509" xlink:to="loc_us-gaap_AssetsCurrent_b45e4ed3-e316-458a-aba1-06af54f58613" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_be5982b4-044e-4d99-919c-b9065f435e5a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d2e5c7a3-0a8e-47d9-b6a6-164c321b23eb" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_be5982b4-044e-4d99-919c-b9065f435e5a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_e3959406-c184-491e-83ea-89f83fd49a4f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_be5982b4-044e-4d99-919c-b9065f435e5a" xlink:to="loc_us-gaap_Goodwill_e3959406-c184-491e-83ea-89f83fd49a4f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxAssetsNet_0408da1b-3154-4bd0-83b3-00ffcde86047" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredIncomeTaxAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_be5982b4-044e-4d99-919c-b9065f435e5a" xlink:to="loc_us-gaap_DeferredIncomeTaxAssetsNet_0408da1b-3154-4bd0-83b3-00ffcde86047" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_a8d34d50-b04e-467d-bb39-18a66ea77dfd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_be5982b4-044e-4d99-919c-b9065f435e5a" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_a8d34d50-b04e-467d-bb39-18a66ea77dfd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentOtherThanNoncurrentInvestmentsAndPropertyPlantAndEquipment_d5ca1dab-b43d-475f-bf4c-8c64417829e0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsNoncurrentOtherThanNoncurrentInvestmentsAndPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_be5982b4-044e-4d99-919c-b9065f435e5a" xlink:to="loc_us-gaap_AssetsNoncurrentOtherThanNoncurrentInvestmentsAndPropertyPlantAndEquipment_d5ca1dab-b43d-475f-bf4c-8c64417829e0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_a7bf46d5-cb2e-46c8-975c-60f4d0ca66a8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_d2e5c7a3-0a8e-47d9-b6a6-164c321b23eb" xlink:to="loc_us-gaap_Assets_a7bf46d5-cb2e-46c8-975c-60f4d0ca66a8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_23aee105-e522-4370-97ce-95720983dd7e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_8ed6a0e5-c581-4902-9961-17892e417932" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_23aee105-e522-4370-97ce-95720983dd7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizationLongtermDebtAndEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_23aee105-e522-4370-97ce-95720983dd7e" xlink:to="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_ee9fe2bf-d8cd-4b36-b20f-40dddac04025" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_CommonStockValue_ee9fe2bf-d8cd-4b36-b20f-40dddac04025" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_12c8692f-985e-4230-82b3-9cadcd0ff1e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_12c8692f-985e-4230-82b3-9cadcd0ff1e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_c645d1b8-d02b-4734-b54a-00effdf02199" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_c645d1b8-d02b-4734-b54a-00effdf02199" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_cd22310d-d92a-4126-b5d5-d6c2e2d5cf27" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_cd22310d-d92a-4126-b5d5-d6c2e2d5cf27" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_3bc1d50a-fdfc-4546-abf2-a1176a16fc05" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_StockholdersEquity_3bc1d50a-fdfc-4546-abf2-a1176a16fc05" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_52b4e6c8-4412-4209-a480-9ffca91df7c3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_52b4e6c8-4412-4209-a480-9ffca91df7c3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_503b2216-85ec-4c11-9cb5-801e46924a34" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_503b2216-85ec-4c11-9cb5-801e46924a34" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizationLongtermDebtAndEquity_80dad232-e104-4bd6-a27c-d90c8782d4dd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalizationLongtermDebtAndEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizationLongtermDebtAndEquityAbstract_9fe443e7-0e3b-4c9f-bdd8-4050f7691386" xlink:to="loc_us-gaap_CapitalizationLongtermDebtAndEquity_80dad232-e104-4bd6-a27c-d90c8782d4dd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_23aee105-e522-4370-97ce-95720983dd7e" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_47055c33-0a82-4b75-a8d7-a4a8605da35c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_LongTermDebtCurrent_47055c33-0a82-4b75-a8d7-a4a8605da35c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_58add016-408b-4340-9321-98174e8b0f2d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_ShortTermBorrowings_58add016-408b-4340-9321-98174e8b0f2d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_0929df65-692b-44a2-bff8-b1d5e976baf4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_AccountsPayableCurrent_0929df65-692b-44a2-bff8-b1d5e976baf4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_016ff531-486a-4b43-8259-966d6c0ea1a7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_016ff531-486a-4b43-8259-966d6c0ea1a7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedIncomeTaxesCurrent_b81c78b0-a348-4a26-be6e-8d63a4e326c7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccruedIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_AccruedIncomeTaxesCurrent_b81c78b0-a348-4a26-be6e-8d63a4e326c7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_9af84cb7-3949-47f5-81a4-6891019d9e2d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_AccrualForTaxesOtherThanIncomeTaxesCurrent_9af84cb7-3949-47f5-81a4-6891019d9e2d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrent_04c9eb04-ce7a-4274-a385-6cc220e753a1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_InterestPayableCurrent_04c9eb04-ce7a-4274-a385-6cc220e753a1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredGasPurchasesCurrent_a1c8694b-6a04-4fe0-9275-cb0d20be3371" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredGasPurchasesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_DeferredGasPurchasesCurrent_a1c8694b-6a04-4fe0-9275-cb0d20be3371" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DueToAffiliateCurrent_f894a68c-8897-4ef5-81e5-00ea74be6a4b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DueToAffiliateCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_DueToAffiliateCurrent_f894a68c-8897-4ef5-81e5-00ea74be6a4b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_8efb5528-68fc-4c60-8619-6c7729b1d258" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_8efb5528-68fc-4c60-8619-6c7729b1d258" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_6ebcad07-16ee-4780-a9b0-616ba4798eb1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_65c31f4c-2968-4984-b905-24c3bb783a07" xlink:to="loc_us-gaap_LiabilitiesCurrent_6ebcad07-16ee-4780-a9b0-616ba4798eb1" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_786ad836-c151-4b07-bea3-e9d57b141c0a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_23aee105-e522-4370-97ce-95720983dd7e" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_786ad836-c151-4b07-bea3-e9d57b141c0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DeferredIncomeTaxesAndUnamortizedInvestmentTaxCredits_de509a0d-6a0f-442a-be6e-4b5259242783" xlink:href="swx-20200630.xsd#swx_DeferredIncomeTaxesAndUnamortizedInvestmentTaxCredits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_786ad836-c151-4b07-bea3-e9d57b141c0a" xlink:to="loc_swx_DeferredIncomeTaxesAndUnamortizedInvestmentTaxCredits_de509a0d-6a0f-442a-be6e-4b5259242783" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesNoncurrent_0ee3d0c4-dc00-4d17-8479-e0251a436dbe" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherAccruedLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_786ad836-c151-4b07-bea3-e9d57b141c0a" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesNoncurrent_0ee3d0c4-dc00-4d17-8479-e0251a436dbe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCreditsAndOtherLiabilitiesNoncurrent_bfcfb33e-2aeb-4d70-b583-7d5793ad0dba" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredCreditsAndOtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_786ad836-c151-4b07-bea3-e9d57b141c0a" xlink:to="loc_us-gaap_DeferredCreditsAndOtherLiabilitiesNoncurrent_bfcfb33e-2aeb-4d70-b583-7d5793ad0dba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_89b7e804-10ce-4c0d-9807-8f096464ee11" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherLiabilitiesNoncurrentAbstract_786ad836-c151-4b07-bea3-e9d57b141c0a" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_89b7e804-10ce-4c0d-9807-8f096464ee11" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_323e99a8-6cbb-48cf-95d3-38df31f3dae8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_23aee105-e522-4370-97ce-95720983dd7e" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_323e99a8-6cbb-48cf-95d3-38df31f3dae8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_24b15466-3f02-4773-a609-dd5589c6417c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_8ed6a0e5-c581-4902-9961-17892e417932" xlink:to="loc_us-gaap_StatementTable_24b15466-3f02-4773-a609-dd5589c6417c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_a46dc2fb-6b66-4d6b-bd3e-9a97c758051b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_24b15466-3f02-4773-a609-dd5589c6417c" xlink:to="loc_dei_LegalEntityAxis_a46dc2fb-6b66-4d6b-bd3e-9a97c758051b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a46dc2fb-6b66-4d6b-bd3e-9a97c758051b_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_a46dc2fb-6b66-4d6b-bd3e-9a97c758051b" xlink:to="loc_dei_EntityDomain_a46dc2fb-6b66-4d6b-bd3e-9a97c758051b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_a3290e19-d867-483d-8e95-263c1b868d64" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_a46dc2fb-6b66-4d6b-bd3e-9a97c758051b" xlink:to="loc_dei_EntityDomain_a3290e19-d867-483d-8e95-263c1b868d64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_9517d98f-bde7-431c-8648-6986b2a1bf4b" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_a3290e19-d867-483d-8e95-263c1b868d64" xlink:to="loc_swx_SouthwestGasCorporationMember_9517d98f-bde7-431c-8648-6986b2a1bf4b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="swx-20200630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended" id="i16b87743fa9149a0bae65042cf730e00_CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOME" xlink:type="simple" xlink:href="swx-20200630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOME"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOME" xlink:type="extended" id="id2e50cd3d8774d3c88646f0814367cac_CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOME">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_0756b02d-eb01-4ce9-8047-3766fbfe2948" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_RevenuesAbstract_0756b02d-eb01-4ce9-8047-3766fbfe2948" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatedOperatingRevenueGas_dc280d11-695f-4f25-9d93-7435a0d7149e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RegulatedOperatingRevenueGas"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_0756b02d-eb01-4ce9-8047-3766fbfe2948" xlink:to="loc_us-gaap_RegulatedOperatingRevenueGas_dc280d11-695f-4f25-9d93-7435a0d7149e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_88ce1cbc-8785-40aa-8b34-c6ed35948df2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_0756b02d-eb01-4ce9-8047-3766fbfe2948" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_88ce1cbc-8785-40aa-8b34-c6ed35948df2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_1f2acbed-afb0-49a5-9f39-fd531738ed53" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RegulatedAndUnregulatedOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_0756b02d-eb01-4ce9-8047-3766fbfe2948" xlink:to="loc_us-gaap_RegulatedAndUnregulatedOperatingRevenue_1f2acbed-afb0-49a5-9f39-fd531738ed53" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased_d4258e1c-a9fb-40fa-8c24-9b3ac9d07680" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseGasAndPetroleumPurchased_d4258e1c-a9fb-40fa-8c24-9b3ac9d07680" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_d4be3485-2001-4615-b611-db906460a1b6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:to="loc_us-gaap_UtilitiesOperatingExpenseMaintenanceAndOperations_d4be3485-2001-4615-b611-db906460a1b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_b14e683f-63e4-4375-b204-92689e79535b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:to="loc_us-gaap_DepreciationAndAmortization_b14e683f-63e4-4375-b204-92689e79535b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_4fb70fe5-e643-455d-93ed-c2fe342ac312" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TaxesExcludingIncomeAndExciseTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:to="loc_us-gaap_TaxesExcludingIncomeAndExciseTaxes_4fb70fe5-e643-455d-93ed-c2fe342ac312" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_72a4a8f8-061c-4b05-a2f9-8a5f40e81983" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_72a4a8f8-061c-4b05-a2f9-8a5f40e81983" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_96850364-ec02-46f0-8cd0-1140245978c3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_f6595649-a45d-4b97-b06e-db14cb3aed90" xlink:to="loc_us-gaap_CostsAndExpenses_96850364-ec02-46f0-8cd0-1140245978c3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_4a44be1b-7dd5-4146-a448-b2aa4fb21870" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_OperatingIncomeLoss_4a44be1b-7dd5-4146-a448-b2aa4fb21870" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_d75a366b-9df7-4971-9d66-4b487884b96b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_d75a366b-9df7-4971-9d66-4b487884b96b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_5e948cbc-edde-438e-b32b-63ca65a887de" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_d75a366b-9df7-4971-9d66-4b487884b96b" xlink:to="loc_us-gaap_InterestExpense_5e948cbc-edde-438e-b32b-63ca65a887de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_270f6d3f-d8b1-42be-9861-d06d2007cd48" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_d75a366b-9df7-4971-9d66-4b487884b96b" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_270f6d3f-d8b1-42be-9861-d06d2007cd48" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_f0e7300a-41bd-4e0c-a4cc-8d673918dd40" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_d75a366b-9df7-4971-9d66-4b487884b96b" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_f0e7300a-41bd-4e0c-a4cc-8d673918dd40" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_3e4a182a-a3e2-44c5-84f1-c0811c70d77a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_3e4a182a-a3e2-44c5-84f1-c0811c70d77a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_4c4458dd-12ad-4e1c-8a31-ac1bc4526758" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_4c4458dd-12ad-4e1c-8a31-ac1bc4526758" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_a2286571-2c69-4c84-82ba-b4c7f61147eb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_ProfitLoss_a2286571-2c69-4c84-82ba-b4c7f61147eb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_5c9583d7-417d-4fd9-98cb-bc2ea7dca6fa" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_5c9583d7-417d-4fd9-98cb-bc2ea7dca6fa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_89d8a2e9-3bb0-4f02-a04e-f7383f2009cb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_NetIncomeLoss_89d8a2e9-3bb0-4f02-a04e-f7383f2009cb" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_7aa093b3-b04d-4bc6-b0d4-0fca054667f9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_EarningsPerShareAbstract_7aa093b3-b04d-4bc6-b0d4-0fca054667f9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_788e55ee-6bfd-455f-80db-df15bde3c52f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_7aa093b3-b04d-4bc6-b0d4-0fca054667f9" xlink:to="loc_us-gaap_EarningsPerShareBasic_788e55ee-6bfd-455f-80db-df15bde3c52f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_fb063743-59da-49f0-a348-4a3b3ed1e214" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_7aa093b3-b04d-4bc6-b0d4-0fca054667f9" xlink:to="loc_us-gaap_EarningsPerShareDiluted_fb063743-59da-49f0-a348-4a3b3ed1e214" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_da1d119a-3ed0-48df-91fb-5fdb472858f6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_da1d119a-3ed0-48df-91fb-5fdb472858f6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b04f7b26-247c-4ea6-b0d8-fbd26121abdd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_da1d119a-3ed0-48df-91fb-5fdb472858f6" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_b04f7b26-247c-4ea6-b0d8-fbd26121abdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_6480021d-0521-4af3-ba3d-c8ee9a182694" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_da1d119a-3ed0-48df-91fb-5fdb472858f6" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_6480021d-0521-4af3-ba3d-c8ee9a182694" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_acc1c054-a6df-4b82-a2fd-637c3487f543" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_fdc0ae50-2cf9-4818-beda-ddc9b1721cf5" xlink:to="loc_us-gaap_StatementTable_acc1c054-a6df-4b82-a2fd-637c3487f543" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_4366e545-2cac-4a17-8be1-ae0d86c17015" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_acc1c054-a6df-4b82-a2fd-637c3487f543" xlink:to="loc_dei_LegalEntityAxis_4366e545-2cac-4a17-8be1-ae0d86c17015" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4366e545-2cac-4a17-8be1-ae0d86c17015_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_4366e545-2cac-4a17-8be1-ae0d86c17015" xlink:to="loc_dei_EntityDomain_4366e545-2cac-4a17-8be1-ae0d86c17015_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_5f57c457-79fb-4007-8ba4-29ddf7aa7b0b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_4366e545-2cac-4a17-8be1-ae0d86c17015" xlink:to="loc_dei_EntityDomain_5f57c457-79fb-4007-8ba4-29ddf7aa7b0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_ec84583e-415d-4b8e-9c55-820f70a639ec" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5f57c457-79fb-4007-8ba4-29ddf7aa7b0b" xlink:to="loc_swx_SouthwestGasCorporationMember_ec84583e-415d-4b8e-9c55-820f70a639ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_0495346b-348a-458e-9788-2149c9429819" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_5f57c457-79fb-4007-8ba4-29ddf7aa7b0b" xlink:to="loc_swx_CenturiGroupInc.Member_0495346b-348a-458e-9788-2149c9429819" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME" xlink:type="simple" xlink:href="swx-20200630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME" xlink:type="extended" id="i21c5dc8d219e495ea1f948a9bb2da749_CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_ac5f5704-7521-46f1-a9c7-2f39ecdad190" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_96d3f280-8cf8-4acd-b85d-b4e6d6db3557" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ac5f5704-7521-46f1-a9c7-2f39ecdad190" xlink:to="loc_us-gaap_ProfitLoss_96d3f280-8cf8-4acd-b85d-b4e6d6db3557" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_a93eaa64-a658-4881-9f63-ff14c12d7e53" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ac5f5704-7521-46f1-a9c7-2f39ecdad190" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_a93eaa64-a658-4881-9f63-ff14c12d7e53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_a93eaa64-a658-4881-9f63-ff14c12d7e53" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_eb76b4d6-b714-4248-b9d7-8956afee612b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodNetOfTax_eb76b4d6-b714-4248-b9d7-8956afee612b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax_4e538861-61fd-4a37-9cad-96bf56748932" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditNetOfTax_4e538861-61fd-4a37-9cad-96bf56748932" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_2cd6842f-467b-4e51-9640-ec5e76483535" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax_2cd6842f-467b-4e51-9640-ec5e76483535" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax_eb8369a9-0252-4065-8b96-ac1db0deaf53" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlanNetPriorServiceCostsCreditArisingDuringPeriodNetOfTax_eb8369a9-0252-4065-8b96-ac1db0deaf53" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherComprehensiveIncomeDefinedBenefitPlansRegulatoryAdjustmentNetOfTax_65ad9dbf-0674-46ad-8b8d-cfa30c0b49d0" xlink:href="swx-20200630.xsd#swx_OtherComprehensiveIncomeDefinedBenefitPlansRegulatoryAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:to="loc_swx_OtherComprehensiveIncomeDefinedBenefitPlansRegulatoryAdjustmentNetOfTax_65ad9dbf-0674-46ad-8b8d-cfa30c0b49d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_dd87793f-5fad-45fa-bfd5-e6dee8ebd1fa" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecreaseAbstract_2c4ad761-f6e0-4589-9124-5ac8c8247f7a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_dd87793f-5fad-45fa-bfd5-e6dee8ebd1fa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_be161f02-49fd-4d23-9b4f-68a616cd6a81" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_a93eaa64-a658-4881-9f63-ff14c12d7e53" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_be161f02-49fd-4d23-9b4f-68a616cd6a81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_bdf58b9f-691f-4327-b0eb-15a766db80ab" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_be161f02-49fd-4d23-9b4f-68a616cd6a81" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_bdf58b9f-691f-4327-b0eb-15a766db80ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_7692187c-f89f-4865-96ca-16b2091b9d71" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecreaseAbstract_be161f02-49fd-4d23-9b4f-68a616cd6a81" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationAndTax_7692187c-f89f-4865-96ca-16b2091b9d71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_a3cadc57-7d0f-4a94-8d4f-29d84cd6ac5f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_a93eaa64-a658-4881-9f63-ff14c12d7e53" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_a3cadc57-7d0f-4a94-8d4f-29d84cd6ac5f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_51be5545-763e-42ea-8233-94329800c828" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterestAbstract_a93eaa64-a658-4881-9f63-ff14c12d7e53" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_51be5545-763e-42ea-8233-94329800c828" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_a0df2efc-604d-413a-908b-83180afb4273" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ac5f5704-7521-46f1-a9c7-2f39ecdad190" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_a0df2efc-604d-413a-908b-83180afb4273" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_52a8f507-dcf0-442c-b45b-7692f6cad84d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ac5f5704-7521-46f1-a9c7-2f39ecdad190" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_52a8f507-dcf0-442c-b45b-7692f6cad84d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_227537eb-f751-4a3d-88f7-6702b56162b2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ac5f5704-7521-46f1-a9c7-2f39ecdad190" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_227537eb-f751-4a3d-88f7-6702b56162b2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_00f44fa5-75ce-4085-a671-2950d71d2b47" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_ac5f5704-7521-46f1-a9c7-2f39ecdad190" xlink:to="loc_us-gaap_StatementTable_00f44fa5-75ce-4085-a671-2950d71d2b47" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_f573b7d4-a839-4801-b5a4-46fb59e2a743" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_00f44fa5-75ce-4085-a671-2950d71d2b47" xlink:to="loc_dei_LegalEntityAxis_f573b7d4-a839-4801-b5a4-46fb59e2a743" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f573b7d4-a839-4801-b5a4-46fb59e2a743_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_f573b7d4-a839-4801-b5a4-46fb59e2a743" xlink:to="loc_dei_EntityDomain_f573b7d4-a839-4801-b5a4-46fb59e2a743_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_df4aacbc-21f9-4ece-b9ce-562d3a805a5c" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_f573b7d4-a839-4801-b5a4-46fb59e2a743" xlink:to="loc_dei_EntityDomain_df4aacbc-21f9-4ece-b9ce-562d3a805a5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_96d1361b-2d1d-4f9c-a406-40af5d11e137" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_df4aacbc-21f9-4ece-b9ce-562d3a805a5c" xlink:to="loc_swx_SouthwestGasCorporationMember_96d1361b-2d1d-4f9c-a406-40af5d11e137" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="simple" xlink:href="swx-20200630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS" xlink:type="extended" id="i9d26b9cde7d54f19a768b0b7ce92848e_CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_1ed93075-a1e0-4ed4-8ad2-24a8f5cfecad" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_1ed93075-a1e0-4ed4-8ad2-24a8f5cfecad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_3c415f9a-9ee6-4d10-9ecb-e7300e969515" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_1ed93075-a1e0-4ed4-8ad2-24a8f5cfecad" xlink:to="loc_us-gaap_ProfitLoss_3c415f9a-9ee6-4d10-9ecb-e7300e969515" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_1ed93075-a1e0-4ed4-8ad2-24a8f5cfecad" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_fa877ed1-a8d0-4fb3-ab64-bc18a6621c70" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_DepreciationAndAmortization_fa877ed1-a8d0-4fb3-ab64-bc18a6621c70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredIncomeTaxes_2b53c6e4-a2e0-4554-bc21-f3b7b9f7e17b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredIncomeTaxes_2b53c6e4-a2e0-4554-bc21-f3b7b9f7e17b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_3099f406-edf7-4a76-922a-b36e525b1dc2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_3099f406-edf7-4a76-922a-b36e525b1dc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_758e8f0a-ff00-4099-9e51-b2091160bf15" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerAsset_758e8f0a-ff00-4099-9e51-b2091160bf15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredGasCost_d12308c9-8911-4f60-92ea-cc160c237c34" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredGasCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredGasCost_d12308c9-8911-4f60-92ea-cc160c237c34" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_281b4413-c635-4cc0-a47f-85dcdb655321" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_281b4413-c635-4cc0-a47f-85dcdb655321" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_IncreaseDecreaseInAccruedTaxes_dd15f025-cfbc-4f00-9ba4-d4e4055b51db" xlink:href="swx-20200630.xsd#swx_IncreaseDecreaseInAccruedTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:to="loc_swx_IncreaseDecreaseInAccruedTaxes_dd15f025-cfbc-4f00-9ba4-d4e4055b51db" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssetsAndLiabilitiesNet_d80d0f7f-45f0-4fc5-9069-8986232174ca" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOtherCurrentAssetsAndLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_24b6c451-6e50-46f3-b88d-9e90f20aa266" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherCurrentAssetsAndLiabilitiesNet_d80d0f7f-45f0-4fc5-9069-8986232174ca" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_58171d65-7eda-4a47-9156-29f1930b73cb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_GainLossOnSaleOfPropertyPlantEquipment_58171d65-7eda-4a47-9156-29f1930b73cb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_ed2f0dba-c3a9-461c-8d22-c3ddffb9f19f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_ShareBasedCompensation_ed2f0dba-c3a9-461c-8d22-c3ddffb9f19f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction_b45d165b-5485-49be-9273-600bbca3504e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_IncreaseDecreaseInAllowanceForEquityFundsUsedDuringConstruction_b45d165b-5485-49be-9273-600bbca3504e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_293d0343-2e63-4121-ae99-e7619cf094ff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_293d0343-2e63-4121-ae99-e7619cf094ff" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_099cda1f-6058-4df5-979d-df86ddb8e349" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_099cda1f-6058-4df5-979d-df86ddb8e349" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_3ecbf12e-342e-4b76-b955-3ed6d40ea293" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_65fdda11-016a-4520-8f56-b34862269d68" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_3ecbf12e-342e-4b76-b955-3ed6d40ea293" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_603cebf1-0db8-4cc3-97de-b60216ba12d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_1ed93075-a1e0-4ed4-8ad2-24a8f5cfecad" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_603cebf1-0db8-4cc3-97de-b60216ba12d0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_436a881d-2fde-475d-b4a9-639596d4138e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_603cebf1-0db8-4cc3-97de-b60216ba12d0" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_436a881d-2fde-475d-b4a9-639596d4138e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_9b9e1390-462e-4233-9267-70abbe9c2400" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_603cebf1-0db8-4cc3-97de-b60216ba12d0" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_9b9e1390-462e-4233-9267-70abbe9c2400" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ChangesInCustomerAdvancesInvestingActivities_3ab4ceec-d207-4b7a-98bc-36123c7792f9" xlink:href="swx-20200630.xsd#swx_ChangesInCustomerAdvancesInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_603cebf1-0db8-4cc3-97de-b60216ba12d0" xlink:to="loc_swx_ChangesInCustomerAdvancesInvestingActivities_3ab4ceec-d207-4b7a-98bc-36123c7792f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_d0c11f43-28d1-4c5a-af64-c34da4de946f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_603cebf1-0db8-4cc3-97de-b60216ba12d0" xlink:to="loc_us-gaap_PaymentsForProceedsFromOtherInvestingActivities_d0c11f43-28d1-4c5a-af64-c34da4de946f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_9b0b6bed-932c-45f1-91c0-87764bc76b01" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_603cebf1-0db8-4cc3-97de-b60216ba12d0" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_9b0b6bed-932c-45f1-91c0-87764bc76b01" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_bbb061cb-f683-4101-b930-bdb9c6f4dae1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_bbb061cb-f683-4101-b930-bdb9c6f4dae1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromContributionsFromParent_5074dc55-eae3-47e7-a534-f16ddd3a7966" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_ProceedsFromContributionsFromParent_5074dc55-eae3-47e7-a534-f16ddd3a7966" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_471dd979-3838-47bc-9d1f-c45f1c0f2cfe" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_471dd979-3838-47bc-9d1f-c45f1c0f2cfe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_ed967ed3-aa86-4070-91ea-81c457359580" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromIssuanceOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfLongTermDebt_ed967ed3-aa86-4070-91ea-81c457359580" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_7f5108e3-a358-47fa-ab0b-a87e992983c9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_7f5108e3-a358-47fa-ab0b-a87e992983c9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ProceedsFromRepaymentsOfLinesOfCreditAndCommercialPaper_65850d71-9f0c-4d22-be4e-b9d889c65149" xlink:href="swx-20200630.xsd#swx_ProceedsFromRepaymentsOfLinesOfCreditAndCommercialPaper"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_swx_ProceedsFromRepaymentsOfLinesOfCreditAndCommercialPaper_65850d71-9f0c-4d22-be4e-b9d889c65149" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebt_e51e3ef0-babd-4758-b7a0-e11ba17d5165" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromRepaymentsOfShortTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebt_e51e3ef0-babd-4758-b7a0-e11ba17d5165" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeasePrincipalPayments_8565af07-55da-454c-b2cb-e1b1211a07c3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinanceLeasePrincipalPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_FinanceLeasePrincipalPayments_8565af07-55da-454c-b2cb-e1b1211a07c3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_c5243999-2813-4f7b-8550-06efc3193259" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_c5243999-2813-4f7b-8550-06efc3193259" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_eef59631-a178-4bcc-80d7-2c369191239e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities_eef59631-a178-4bcc-80d7-2c369191239e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_40cdf800-bddd-4868-8610-48277cdd25f3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_8ee13588-e38e-48f0-8fca-9e04905b26cb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_40cdf800-bddd-4868-8610-48277cdd25f3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_abf36531-e052-4259-94d9-8024c7636e6e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_abf36531-e052-4259-94d9-8024c7636e6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_6eadf7ca-4af0-4f43-b597-9ffec754204d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_6eadf7ca-4af0-4f43-b597-9ffec754204d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_7ec6d930-623e-4707-be8f-5612eda82dfa" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_7ec6d930-623e-4707-be8f-5612eda82dfa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_6b2cb9d6-2210-4e72-abef-201f36b177fb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_ed3a15ce-28e7-4ec0-9afd-e9b9adb78f51" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_ed3a15ce-28e7-4ec0-9afd-e9b9adb78f51" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_263652e8-41b0-4dbd-9c5c-3f9be7c36539" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_ed3a15ce-28e7-4ec0-9afd-e9b9adb78f51" xlink:to="loc_us-gaap_InterestPaidNet_263652e8-41b0-4dbd-9c5c-3f9be7c36539" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_ff3e57d1-1f7a-4d0e-a537-6ec6e7f95a0e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_ed3a15ce-28e7-4ec0-9afd-e9b9adb78f51" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_ff3e57d1-1f7a-4d0e-a537-6ec6e7f95a0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_fa487b95-8e18-41fa-af3c-a7942f140b5f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_292e104b-eb6f-4a90-bde7-a85c4d88b569" xlink:to="loc_us-gaap_StatementTable_fa487b95-8e18-41fa-af3c-a7942f140b5f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1c3bd458-b48b-4584-8711-dffd6ffa4263" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_fa487b95-8e18-41fa-af3c-a7942f140b5f" xlink:to="loc_dei_LegalEntityAxis_1c3bd458-b48b-4584-8711-dffd6ffa4263" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1c3bd458-b48b-4584-8711-dffd6ffa4263_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1c3bd458-b48b-4584-8711-dffd6ffa4263" xlink:to="loc_dei_EntityDomain_1c3bd458-b48b-4584-8711-dffd6ffa4263_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_7e20356e-adce-4216-b7a3-e01279ea19d4" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1c3bd458-b48b-4584-8711-dffd6ffa4263" xlink:to="loc_dei_EntityDomain_7e20356e-adce-4216-b7a3-e01279ea19d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_084dd5e2-5fe6-4e2a-b597-6ee4b1a146c0" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_7e20356e-adce-4216-b7a3-e01279ea19d4" xlink:to="loc_swx_SouthwestGasCorporationMember_084dd5e2-5fe6-4e2a-b597-6ee4b1a146c0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY" xlink:type="simple" xlink:href="swx-20200630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY" xlink:type="extended" id="i86d7395a0676411582bc82160823f0c1_CONDENSEDCONSOLIDATEDSTATEMENTSOFEQUITY">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_d449cd5f-f877-42fe-89ff-d1a81190a6bf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d449cd5f-f877-42fe-89ff-d1a81190a6bf" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_6bb267e1-6eca-472f-9868-746b8a9fec83" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_6bb267e1-6eca-472f-9868-746b8a9fec83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_5dbdf7ea-84ac-4088-a729-6deb83eaa796" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_5dbdf7ea-84ac-4088-a729-6deb83eaa796" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_1f970fde-c925-4aac-8a32-01cada5762df" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_1f970fde-c925-4aac-8a32-01cada5762df" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_ad616050-145d-48f2-b40c-a63e055c7252" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_ad616050-145d-48f2-b40c-a63e055c7252" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_98251e3d-4cb0-41e1-83fe-f30042cc3aaf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_98251e3d-4cb0-41e1-83fe-f30042cc3aaf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent_f5f6273e-8d7c-424f-be6a-0dd3b528ef2c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxPortionAttributableToParent_f5f6273e-8d7c-424f-be6a-0dd3b528ef2c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther_2aa2db81-512a-40dd-ae40-155c28354c1e" xlink:href="swx-20200630.xsd#swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_swx_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTaxOther_2aa2db81-512a-40dd-ae40-155c28354c1e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_08957d37-62a7-4702-909c-37739fddbf13" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationAfterTax_08957d37-62a7-4702-909c-37739fddbf13" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_fc63a2ed-3e7a-40fc-8568-e88453d4befb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_NetIncomeLossIncludingPortionAttributableToNonredeemableNoncontrollingInterest_fc63a2ed-3e7a-40fc-8568-e88453d4befb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_7d3f1148-04d0-4764-9d49-c80d70d41e9e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_7d3f1148-04d0-4764-9d49-c80d70d41e9e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AdjustmentsToAdditionalPaidInCapitalContributionsFromParent_1d269c4f-f466-460f-8e79-c9aa3d5b3532" xlink:href="swx-20200630.xsd#swx_AdjustmentsToAdditionalPaidInCapitalContributionsFromParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_swx_AdjustmentsToAdditionalPaidInCapitalContributionsFromParent_1d269c4f-f466-460f-8e79-c9aa3d5b3532" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStock_1edd10b2-4fd2-472d-9d5c-d2f1ca70149f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_b307c051-45bf-4417-a4eb-99b62693445a" xlink:to="loc_us-gaap_DividendsCommonStock_1edd10b2-4fd2-472d-9d5c-d2f1ca70149f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_d6e8571f-1ff8-4fb4-8e26-61b29ec10ec5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_b0a5a3da-6586-42b2-8bdb-42fe622b1c24" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_318e70fd-79f2-43ec-96f7-761a54e9ed6c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_d449cd5f-f877-42fe-89ff-d1a81190a6bf" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_318e70fd-79f2-43ec-96f7-761a54e9ed6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_1a8321ba-a08b-49eb-8916-517e45d2a741" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_d449cd5f-f877-42fe-89ff-d1a81190a6bf" xlink:to="loc_us-gaap_StatementTable_1a8321ba-a08b-49eb-8916-517e45d2a741" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_2828f70b-269f-418f-b838-d0401358793c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1a8321ba-a08b-49eb-8916-517e45d2a741" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_2828f70b-269f-418f-b838-d0401358793c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2828f70b-269f-418f-b838-d0401358793c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_2828f70b-269f-418f-b838-d0401358793c" xlink:to="loc_us-gaap_EquityComponentDomain_2828f70b-269f-418f-b838-d0401358793c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_2828f70b-269f-418f-b838-d0401358793c" xlink:to="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_e77429d1-7bb0-47a4-949d-0f88d27080bf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:to="loc_us-gaap_CommonStockMember_e77429d1-7bb0-47a4-949d-0f88d27080bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_a7312266-63eb-4b19-959a-ed8c85998dd5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_a7312266-63eb-4b19-959a-ed8c85998dd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_365d9bdd-307c-4d61-9ce6-754c464d150e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_365d9bdd-307c-4d61-9ce6-754c464d150e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_724cda9f-941e-4881-91f4-30864bd0734a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:to="loc_us-gaap_RetainedEarningsMember_724cda9f-941e-4881-91f4-30864bd0734a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_937f151d-1655-4c37-a977-76098eaf7447" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:to="loc_us-gaap_ParentMember_937f151d-1655-4c37-a977-76098eaf7447" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_0d00b71c-03ce-499f-89e4-7986220ef772" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_734d867c-57a5-49f5-944c-5da55f6c70fa" xlink:to="loc_us-gaap_NoncontrollingInterestMember_0d00b71c-03ce-499f-89e4-7986220ef772" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_870681d0-defa-4db7-a14c-7a5d3b3f179a" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1a8321ba-a08b-49eb-8916-517e45d2a741" xlink:to="loc_dei_LegalEntityAxis_870681d0-defa-4db7-a14c-7a5d3b3f179a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_870681d0-defa-4db7-a14c-7a5d3b3f179a_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_870681d0-defa-4db7-a14c-7a5d3b3f179a" xlink:to="loc_dei_EntityDomain_870681d0-defa-4db7-a14c-7a5d3b3f179a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_9fd1a3bc-cc7d-408d-ab4c-024912d1a417" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_870681d0-defa-4db7-a14c-7a5d3b3f179a" xlink:to="loc_dei_EntityDomain_9fd1a3bc-cc7d-408d-ab4c-024912d1a417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_c9757758-fafa-4806-91a8-41cc5d4df937" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9fd1a3bc-cc7d-408d-ab4c-024912d1a417" xlink:to="loc_swx_SouthwestGasCorporationMember_c9757758-fafa-4806-91a8-41cc5d4df937" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPolicies" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPolicies"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPolicies" xlink:type="extended" id="ieaf9f39fa53b4404a6a074e3e21b2cf1_BackgroundOrganizationandSummaryofSignificantAccountingPolicies"/>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesPolicies" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesPolicies"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesPolicies" xlink:type="extended" id="icea5fa94d58d4493931fb2d706710d65_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesPolicies"/>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesTables" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesTables"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesTables" xlink:type="extended" id="ibf74a509c07f4ffc9097905717ae3094_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesTables"/>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofOtherPropertyandInvestmentsDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofOtherPropertyandInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofOtherPropertyandInvestmentsDetails" xlink:type="extended" id="i95c689db2ee3474fbabbd4fb0b91c8c8_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofOtherPropertyandInvestmentsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_221d1934-2bc8-46c4-855f-76ecdcfcd205" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashSurrenderValueOfLifeInsurance_1dfc4eee-0111-4047-b945-791f802e18fb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashSurrenderValueOfLifeInsurance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_221d1934-2bc8-46c4-855f-76ecdcfcd205" xlink:to="loc_us-gaap_CashSurrenderValueOfLifeInsurance_1dfc4eee-0111-4047-b945-791f802e18fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentOtherNet_f3b5c1e7-9f05-44fd-97bc-62e0509fb53c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentOtherNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_221d1934-2bc8-46c4-855f-76ecdcfcd205" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentOtherNet_f3b5c1e7-9f05-44fd-97bc-62e0509fb53c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherPropertyAndInvestments_1b9c4d69-3b23-4882-bd94-b032fd394416" xlink:href="swx-20200630.xsd#swx_OtherPropertyAndInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_221d1934-2bc8-46c4-855f-76ecdcfcd205" xlink:to="loc_swx_OtherPropertyAndInvestments_1b9c4d69-3b23-4882-bd94-b032fd394416" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_PropertyPlantEquipmentAndIntangibleAssetsGross_4756e3a0-5745-4802-bd74-5479bb37aa5c" xlink:href="swx-20200630.xsd#swx_PropertyPlantEquipmentAndIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_221d1934-2bc8-46c4-855f-76ecdcfcd205" xlink:to="loc_swx_PropertyPlantEquipmentAndIntangibleAssetsGross_4756e3a0-5745-4802-bd74-5479bb37aa5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_c52fb9ec-fc95-41ac-805b-614582a90db0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_221d1934-2bc8-46c4-855f-76ecdcfcd205" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_c52fb9ec-fc95-41ac-805b-614582a90db0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_bad449c0-e599-493c-b9c0-aa2753db5db9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_221d1934-2bc8-46c4-855f-76ecdcfcd205" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_bad449c0-e599-493c-b9c0-aa2753db5db9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_254a1c38-9079-4fed-aa48-2c6fdfb406c6" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_bad449c0-e599-493c-b9c0-aa2753db5db9" xlink:to="loc_dei_LegalEntityAxis_254a1c38-9079-4fed-aa48-2c6fdfb406c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_254a1c38-9079-4fed-aa48-2c6fdfb406c6_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_254a1c38-9079-4fed-aa48-2c6fdfb406c6" xlink:to="loc_dei_EntityDomain_254a1c38-9079-4fed-aa48-2c6fdfb406c6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_83385a7e-5195-4efd-aa74-ba053e7b736f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_254a1c38-9079-4fed-aa48-2c6fdfb406c6" xlink:to="loc_dei_EntityDomain_83385a7e-5195-4efd-aa74-ba053e7b736f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_36da29af-e442-4779-acdf-514e77edfa4a" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_83385a7e-5195-4efd-aa74-ba053e7b736f" xlink:to="loc_swx_SouthwestGasCorporationMember_36da29af-e442-4779-acdf-514e77edfa4a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_c9658203-1c5e-4a47-ba22-efe1df562aef" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_83385a7e-5195-4efd-aa74-ba053e7b736f" xlink:to="loc_swx_CenturiGroupInc.Member_c9658203-1c5e-4a47-ba22-efe1df562aef" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetails" xlink:type="extended" id="i12f1a8a9404a49a0904bcd92f7e29dd5_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:href="swx-20200630.xsd#swx_SignificantAccountingPoliciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_33d4a802-df21-41f2-95be-a5e95b613e28" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_33d4a802-df21-41f2-95be-a5e95b613e28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfStatesInWhichEntityOperates_155152ad-952e-47f0-9c9d-00e6938e867b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NumberOfStatesInWhichEntityOperates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_NumberOfStatesInWhichEntityOperates_155152ad-952e-47f0-9c9d-00e6938e867b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable_f875303e-60cb-451c-bdf2-1fea65b962f7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_ThresholdPeriodPastDueForWriteoffOfTradeAccountsReceivable_f875303e-60cb-451c-bdf2-1fea65b962f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialsSuppliesAndOther_4da3f2df-ab32-43be-9cf5-e646f5263d92" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MaterialsSuppliesAndOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_MaterialsSuppliesAndOther_4da3f2df-ab32-43be-9cf5-e646f5263d92" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatoryAssetsCurrent_d607337a-1f09-415d-a524-f8ba0eff56bd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RegulatoryAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_RegulatoryAssetsCurrent_d607337a-1f09-415d-a524-f8ba0eff56bd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_79d5ad0f-ae9f-4296-9db5-97fef46a377c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_79d5ad0f-ae9f-4296-9db5-97fef46a377c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrent_f2cfdc44-10d6-4108-8e5c-7e96f27d1ce8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DividendsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_DividendsPayableCurrent_f2cfdc44-10d6-4108-8e5c-7e96f27d1ce8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_784697b8-0bbc-46c6-b096-6ec6cf08c950" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_784697b8-0bbc-46c6-b096-6ec6cf08c950" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SignificantAccountingPoliciesTable_0aa73267-1bec-4cbb-8083-9e320ac170bd" xlink:href="swx-20200630.xsd#swx_SignificantAccountingPoliciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_swx_SignificantAccountingPoliciesLineItems_41baf09a-a849-4200-af74-ce80f71654cb" xlink:to="loc_swx_SignificantAccountingPoliciesTable_0aa73267-1bec-4cbb-8083-9e320ac170bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_0cf20568-e582-4570-b899-b6f7e748590e" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_0aa73267-1bec-4cbb-8083-9e320ac170bd" xlink:to="loc_dei_LegalEntityAxis_0cf20568-e582-4570-b899-b6f7e748590e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0cf20568-e582-4570-b899-b6f7e748590e_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_0cf20568-e582-4570-b899-b6f7e748590e" xlink:to="loc_dei_EntityDomain_0cf20568-e582-4570-b899-b6f7e748590e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_15573a5a-10bd-43e6-a071-7f2491c8b9a7" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_0cf20568-e582-4570-b899-b6f7e748590e" xlink:to="loc_dei_EntityDomain_15573a5a-10bd-43e6-a071-7f2491c8b9a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_2f60cf6a-6d1c-4faf-b704-ca9b54b20d67" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_15573a5a-10bd-43e6-a071-7f2491c8b9a7" xlink:to="loc_swx_CenturiGroupInc.Member_2f60cf6a-6d1c-4faf-b704-ca9b54b20d67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_a2fb89a5-f291-4f21-85ce-9893acbd8a50" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_15573a5a-10bd-43e6-a071-7f2491c8b9a7" xlink:to="loc_swx_SouthwestGasCorporationMember_a2fb89a5-f291-4f21-85ce-9893acbd8a50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_d2126b25-7af5-40b2-bfca-d137d3bd99a1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_0aa73267-1bec-4cbb-8083-9e320ac170bd" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_d2126b25-7af5-40b2-bfca-d137d3bd99a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_d2126b25-7af5-40b2-bfca-d137d3bd99a1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_d2126b25-7af5-40b2-bfca-d137d3bd99a1" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_d2126b25-7af5-40b2-bfca-d137d3bd99a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_7134f4b5-d2e6-4a88-bd5b-3105d1d6dfd9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_d2126b25-7af5-40b2-bfca-d137d3bd99a1" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_7134f4b5-d2e6-4a88-bd5b-3105d1d6dfd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_5b0178e4-1d58-449b-8e77-d39e4698133c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_7134f4b5-d2e6-4a88-bd5b-3105d1d6dfd9" xlink:to="loc_us-gaap_MoneyMarketFundsMember_5b0178e4-1d58-449b-8e77-d39e4698133c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryAxis_2c7876da-fa4c-4944-a95b-6c56ff3a7475" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesInventoryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_0aa73267-1bec-4cbb-8083-9e320ac170bd" xlink:to="loc_us-gaap_PublicUtilitiesInventoryAxis_2c7876da-fa4c-4944-a95b-6c56ff3a7475" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_2c7876da-fa4c-4944-a95b-6c56ff3a7475_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_2c7876da-fa4c-4944-a95b-6c56ff3a7475" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_2c7876da-fa4c-4944-a95b-6c56ff3a7475_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_50b75112-2c8f-4c9a-8865-12aaf0490e1f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_2c7876da-fa4c-4944-a95b-6c56ff3a7475" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_50b75112-2c8f-4c9a-8865-12aaf0490e1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_GasPipeInventoryAndOperatingSuppliesMember_dbd21663-339b-4826-aa71-dad9a8e65cfd" xlink:href="swx-20200630.xsd#swx_GasPipeInventoryAndOperatingSuppliesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_50b75112-2c8f-4c9a-8865-12aaf0490e1f" xlink:to="loc_swx_GasPipeInventoryAndOperatingSuppliesMember_dbd21663-339b-4826-aa71-dad9a8e65cfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_c6330ea2-7f81-4d03-b142-689b0e8a3bd4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_0aa73267-1bec-4cbb-8083-9e320ac170bd" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_c6330ea2-7f81-4d03-b142-689b0e8a3bd4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_c6330ea2-7f81-4d03-b142-689b0e8a3bd4_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_c6330ea2-7f81-4d03-b142-689b0e8a3bd4" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_c6330ea2-7f81-4d03-b142-689b0e8a3bd4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_588e1051-20d7-4097-9ed6-96790c9085ab" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_c6330ea2-7f81-4d03-b142-689b0e8a3bd4" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_588e1051-20d7-4097-9ed6-96790c9085ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_9863b694-1a66-439a-8b69-ca6c5dd6e36a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_588e1051-20d7-4097-9ed6-96790c9085ab" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_9863b694-1a66-439a-8b69-ca6c5dd6e36a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_e9702acf-08ef-4f21-a657-4d93af62818e" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_swx_SignificantAccountingPoliciesTable_0aa73267-1bec-4cbb-8083-9e320ac170bd" xlink:to="loc_srt_OwnershipAxis_e9702acf-08ef-4f21-a657-4d93af62818e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_e9702acf-08ef-4f21-a657-4d93af62818e_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_e9702acf-08ef-4f21-a657-4d93af62818e" xlink:to="loc_srt_OwnershipDomain_e9702acf-08ef-4f21-a657-4d93af62818e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_b655d093-4f95-4657-834a-524471560896" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_e9702acf-08ef-4f21-a657-4d93af62818e" xlink:to="loc_srt_OwnershipDomain_b655d093-4f95-4657-834a-524471560896" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LinetecServicesLLCMember_8df6cc47-89a4-49c0-a9f2-5a2a0be20243" xlink:href="swx-20200630.xsd#swx_LinetecServicesLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_b655d093-4f95-4657-834a-524471560896" xlink:to="loc_swx_LinetecServicesLLCMember_8df6cc47-89a4-49c0-a9f2-5a2a0be20243" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofGoodwillDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofGoodwillDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofGoodwillDetails" xlink:type="extended" id="i5caacf5f0e9d4d63956e893ac54ad924_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofGoodwillDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_d2d5b59b-0604-494a-8ff9-86f34c85e1f5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_1bb0529d-9154-400b-927e-38a4e95fab88" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_d2d5b59b-0604-494a-8ff9-86f34c85e1f5" xlink:to="loc_us-gaap_GoodwillRollForward_1bb0529d-9154-400b-927e-38a4e95fab88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_c2f562be-14ca-401c-9df6-973cf7a3d1a7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_1bb0529d-9154-400b-927e-38a4e95fab88" xlink:to="loc_us-gaap_Goodwill_c2f562be-14ca-401c-9df6-973cf7a3d1a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_739ed5ad-ffc6-43ef-9ab8-5d6f0be61813" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_1bb0529d-9154-400b-927e-38a4e95fab88" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_739ed5ad-ffc6-43ef-9ab8-5d6f0be61813" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_69582331-ee2e-466e-84a7-b1d947f94190" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_913d7f1a-090b-47b6-920f-34ee2b6d14d0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_d2d5b59b-0604-494a-8ff9-86f34c85e1f5" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_913d7f1a-090b-47b6-920f-34ee2b6d14d0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_758c42c1-300b-4f19-b9a0-b2ee3569466f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_913d7f1a-090b-47b6-920f-34ee2b6d14d0" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_758c42c1-300b-4f19-b9a0-b2ee3569466f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_758c42c1-300b-4f19-b9a0-b2ee3569466f_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_758c42c1-300b-4f19-b9a0-b2ee3569466f" xlink:to="loc_us-gaap_SegmentDomain_758c42c1-300b-4f19-b9a0-b2ee3569466f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4fa68599-22dd-43cf-8b97-16e07710a978" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_758c42c1-300b-4f19-b9a0-b2ee3569466f" xlink:to="loc_us-gaap_SegmentDomain_4fa68599-22dd-43cf-8b97-16e07710a978" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_NaturalGasOperationsMember_b097e4d9-d84c-4f2e-a474-70c7c4a29c01" xlink:href="swx-20200630.xsd#swx_NaturalGasOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4fa68599-22dd-43cf-8b97-16e07710a978" xlink:to="loc_swx_NaturalGasOperationsMember_b097e4d9-d84c-4f2e-a474-70c7c4a29c01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UtilityInfrastructureServicesSegmentMember_47bfda13-4c37-4f0d-8aa1-92a2a011b1bc" xlink:href="swx-20200630.xsd#swx_UtilityInfrastructureServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4fa68599-22dd-43cf-8b97-16e07710a978" xlink:to="loc_swx_UtilityInfrastructureServicesSegmentMember_47bfda13-4c37-4f0d-8aa1-92a2a011b1bc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesOtherIncomeDeductionsDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesOtherIncomeDeductionsDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesOtherIncomeDeductionsDetails" xlink:type="extended" id="i118e8db2f3e341b98a19e028592544a2_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesOtherIncomeDeductionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedIncomeStatementsCaptionsLineItems_57862df8-d748-483e-92bf-2a4609e458ed" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedIncomeStatementsCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CondensedIncomeStatementsCaptionsLineItems_57862df8-d748-483e-92bf-2a4609e458ed" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue_7cf745c4-8a2d-4011-9e18-6ec136967d0d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:to="loc_us-gaap_LifeInsuranceCorporateOrBankOwnedChangeInValue_7cf745c4-8a2d-4011-9e18-6ec136967d0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOther_92f5de59-e27a-4619-988b-e5b8eb3da2ce" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:to="loc_us-gaap_InterestIncomeOther_92f5de59-e27a-4619-988b-e5b8eb3da2ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_fdc2af54-7578-45dc-838e-220aa714f2ec" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:to="loc_us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity_fdc2af54-7578-45dc-838e-220aa714f2ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_8e0b8c69-cb1d-4397-9445-8731c7c1e473" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_8e0b8c69-cb1d-4397-9445-8731c7c1e473" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit_636f0ee9-5493-47d1-a2e0-a9b4ffa94999" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:to="loc_us-gaap_DefinedBenefitPlanActuarialGainLossImmediateRecognitionAsComponentInNetPeriodicBenefitCostCredit_636f0ee9-5493-47d1-a2e0-a9b4ffa94999" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_MiscellaneousIncomeExpense_8084499f-e0ae-4937-8ead-e3f8c6b25291" xlink:href="swx-20200630.xsd#swx_MiscellaneousIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:to="loc_swx_MiscellaneousIncomeExpense_8084499f-e0ae-4937-8ead-e3f8c6b25291" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_00118058-8105-4dc1-9e09-97f1738e9042" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_d9c21b33-a947-45da-9bc4-56636489fcb1" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_00118058-8105-4dc1-9e09-97f1738e9042" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CondensedIncomeStatementTable_c3a78a93-14e5-49eb-98a3-9d53260c75ae" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedIncomeStatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_CondensedIncomeStatementsCaptionsLineItems_57862df8-d748-483e-92bf-2a4609e458ed" xlink:to="loc_srt_CondensedIncomeStatementTable_c3a78a93-14e5-49eb-98a3-9d53260c75ae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_b95813df-a086-47f5-8add-b010dcd9cdb8" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_CondensedIncomeStatementTable_c3a78a93-14e5-49eb-98a3-9d53260c75ae" xlink:to="loc_srt_ConsolidationItemsAxis_b95813df-a086-47f5-8add-b010dcd9cdb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_b95813df-a086-47f5-8add-b010dcd9cdb8_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_b95813df-a086-47f5-8add-b010dcd9cdb8" xlink:to="loc_srt_ConsolidationItemsDomain_b95813df-a086-47f5-8add-b010dcd9cdb8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_2dbe7f18-3564-486e-8cec-02081bf29448" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_b95813df-a086-47f5-8add-b010dcd9cdb8" xlink:to="loc_srt_ConsolidationItemsDomain_2dbe7f18-3564-486e-8cec-02081bf29448" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_30f71bf3-353c-46e4-a5fc-0b5ca07e7bc1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2dbe7f18-3564-486e-8cec-02081bf29448" xlink:to="loc_us-gaap_OperatingSegmentsMember_30f71bf3-353c-46e4-a5fc-0b5ca07e7bc1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_9a71afcf-a972-49ee-bd3b-0a91aac26712" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2dbe7f18-3564-486e-8cec-02081bf29448" xlink:to="loc_us-gaap_CorporateNonSegmentMember_9a71afcf-a972-49ee-bd3b-0a91aac26712" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_ecd66598-76ff-4476-be6a-48a992c66127" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_CondensedIncomeStatementTable_c3a78a93-14e5-49eb-98a3-9d53260c75ae" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_ecd66598-76ff-4476-be6a-48a992c66127" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_ecd66598-76ff-4476-be6a-48a992c66127_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ecd66598-76ff-4476-be6a-48a992c66127" xlink:to="loc_us-gaap_SegmentDomain_ecd66598-76ff-4476-be6a-48a992c66127_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_523bc705-ff6b-4f39-9e9e-5183d904bba2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ecd66598-76ff-4476-be6a-48a992c66127" xlink:to="loc_us-gaap_SegmentDomain_523bc705-ff6b-4f39-9e9e-5183d904bba2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_NaturalGasOperationsMember_34ce49bf-ee7a-4f28-bc92-01022bf13dbe" xlink:href="swx-20200630.xsd#swx_NaturalGasOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_523bc705-ff6b-4f39-9e9e-5183d904bba2" xlink:to="loc_swx_NaturalGasOperationsMember_34ce49bf-ee7a-4f28-bc92-01022bf13dbe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UtilityInfrastructureServicesSegmentMember_c57339a8-76d8-4aac-8532-5bb9de86641d" xlink:href="swx-20200630.xsd#swx_UtilityInfrastructureServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_523bc705-ff6b-4f39-9e9e-5183d904bba2" xlink:to="loc_swx_UtilityInfrastructureServicesSegmentMember_c57339a8-76d8-4aac-8532-5bb9de86641d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_61755bf3-5855-4af8-96b3-97e6a7f7c976" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_CondensedIncomeStatementTable_c3a78a93-14e5-49eb-98a3-9d53260c75ae" xlink:to="loc_dei_LegalEntityAxis_61755bf3-5855-4af8-96b3-97e6a7f7c976" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_61755bf3-5855-4af8-96b3-97e6a7f7c976_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_61755bf3-5855-4af8-96b3-97e6a7f7c976" xlink:to="loc_dei_EntityDomain_61755bf3-5855-4af8-96b3-97e6a7f7c976_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_3c209972-f48b-4b81-8545-92765724279d" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_61755bf3-5855-4af8-96b3-97e6a7f7c976" xlink:to="loc_dei_EntityDomain_3c209972-f48b-4b81-8545-92765724279d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_4a1f528d-88da-477c-b9d5-40d82cd6ef1b" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3c209972-f48b-4b81-8545-92765724279d" xlink:to="loc_swx_SouthwestGasCorporationMember_4a1f528d-88da-477c-b9d5-40d82cd6ef1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_582882d9-e3cd-4b3b-963e-b414acda2776" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_3c209972-f48b-4b81-8545-92765724279d" xlink:to="loc_swx_CenturiGroupInc.Member_582882d9-e3cd-4b3b-963e-b414acda2776" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesSummaryofRedeemableNoncontrollingInterestDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesSummaryofRedeemableNoncontrollingInterestDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesSummaryofRedeemableNoncontrollingInterestDetails" xlink:type="extended" id="i15fd2db4ccfc4c21855746148b5f2c10_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesSummaryofRedeemableNoncontrollingInterestDetails"/>
  <link:roleRef roleURI="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesBackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofEarningsPerShareDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#BackgroundOrganizationandSummaryofSignificantAccountingPoliciesBackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/BackgroundOrganizationandSummaryofSignificantAccountingPoliciesBackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofEarningsPerShareDetails" xlink:type="extended" id="ia6b60f5894664a50b29fa08883d31f8e_BackgroundOrganizationandSummaryofSignificantAccountingPoliciesBackgroundOrganizationandSummaryofSignificantAccountingPoliciesScheduleofEarningsPerShareDetails"/>
  <link:roleRef roleURI="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCost" xlink:type="simple" xlink:href="swx-20200630.xsd#ComponentsofNetPeriodicBenefitCost"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCost" xlink:type="extended" id="i9d3249afa289437db99e2738dd2d7e3e_ComponentsofNetPeriodicBenefitCost"/>
  <link:roleRef roleURI="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCostTables" xlink:type="simple" xlink:href="swx-20200630.xsd#ComponentsofNetPeriodicBenefitCostTables"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCostTables" xlink:type="extended" id="i7183527e5b554ff784b24cc8e03bb4fb_ComponentsofNetPeriodicBenefitCostTables"/>
  <link:roleRef roleURI="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCostDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#ComponentsofNetPeriodicBenefitCostDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/ComponentsofNetPeriodicBenefitCostDetails" xlink:type="extended" id="i907fbb38d56e4df0b0850a3d97e5d4c5_ComponentsofNetPeriodicBenefitCostDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanServiceCost_2a38412b-15ac-4085-9bf2-0fba297316e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:to="loc_us-gaap_DefinedBenefitPlanServiceCost_2a38412b-15ac-4085-9bf2-0fba297316e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanInterestCost_a8052928-143b-4661-8265-2fcc7cf84a7a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:to="loc_us-gaap_DefinedBenefitPlanInterestCost_a8052928-143b-4661-8265-2fcc7cf84a7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_bcadf3a8-cafa-4016-b687-3f9f2935ddc0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets_bcadf3a8-cafa-4016-b687-3f9f2935ddc0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_f6f073b2-0c89-464c-87b1-0fc6c08d40b5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses_f6f073b2-0c89-464c-87b1-0fc6c08d40b5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_c5e392ad-da7a-4bde-9060-d3393f0d351e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:to="loc_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit_c5e392ad-da7a-4bde-9060-d3393f0d351e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_5148229c-8c75-4b98-9001-35c01b67f1d6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:to="loc_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost_5148229c-8c75-4b98-9001-35c01b67f1d6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_477d045d-eb1a-4a81-9457-d3c0e1025b62" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_cc6e369d-7a08-40d3-be08-d06a2634ae25" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_477d045d-eb1a-4a81-9457-d3c0e1025b62" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeAxis_049e2f11-4b01-4b6a-aff6-8018d5ba6732" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_477d045d-eb1a-4a81-9457-d3c0e1025b62" xlink:to="loc_us-gaap_RetirementPlanTypeAxis_049e2f11-4b01-4b6a-aff6-8018d5ba6732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_049e2f11-4b01-4b6a-aff6-8018d5ba6732_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_049e2f11-4b01-4b6a-aff6-8018d5ba6732" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_049e2f11-4b01-4b6a-aff6-8018d5ba6732_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanTypeDomain_cb52801d-859c-4ebc-abc3-d82da097c906" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanTypeAxis_049e2f11-4b01-4b6a-aff6-8018d5ba6732" xlink:to="loc_us-gaap_RetirementPlanTypeDomain_cb52801d-859c-4ebc-abc3-d82da097c906" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPensionPlansDefinedBenefitMember_aa44c451-2738-4786-93d6-8acab910d68c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherPensionPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_cb52801d-859c-4ebc-abc3-d82da097c906" xlink:to="loc_us-gaap_OtherPensionPlansDefinedBenefitMember_aa44c451-2738-4786-93d6-8acab910d68c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_1a76005c-72b1-40be-a220-6b72330cc7b1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_cb52801d-859c-4ebc-abc3-d82da097c906" xlink:to="loc_us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember_1a76005c-72b1-40be-a220-6b72330cc7b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_6786d09b-eb85-4682-bf61-f90b33215ee7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanTypeDomain_cb52801d-859c-4ebc-abc3-d82da097c906" xlink:to="loc_us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember_6786d09b-eb85-4682-bf61-f90b33215ee7" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/Revenue" xlink:type="simple" xlink:href="swx-20200630.xsd#Revenue"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/Revenue" xlink:type="extended" id="i49d1e1d8647040fab704805da0bf3631_Revenue"/>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueTables" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueTables"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueTables" xlink:type="extended" id="i191148637e8c484baaaa8c450a1ac9dc_RevenueTables"/>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueAdditionalInformationDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueAdditionalInformationDetails" xlink:type="extended" id="i5cce630f186d462eb7b27f9ed10a9f10_RevenueAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_896bc7a0-bfca-450b-8dee-8b3b554b6e83" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_077a210f-8318-4933-8221-0e31027facf9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_896bc7a0-bfca-450b-8dee-8b3b554b6e83" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_077a210f-8318-4933-8221-0e31027facf9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear_e982bd94-55fb-4c61-b6e7-a278169e8070" xlink:href="swx-20200630.xsd#swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_896bc7a0-bfca-450b-8dee-8b3b554b6e83" xlink:to="loc_swx_RevenueRecognitionNumberOfContractsWithOriginalDurationMoreThanOneYear_e982bd94-55fb-4c61-b6e7-a278169e8070" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e37a7084-4b37-46fb-b542-23ed499a64cc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_896bc7a0-bfca-450b-8dee-8b3b554b6e83" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e37a7084-4b37-46fb-b542-23ed499a64cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_d4330ea9-d9d4-4e7c-b9fb-34ee23b83558" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e37a7084-4b37-46fb-b542-23ed499a64cc" xlink:to="loc_dei_LegalEntityAxis_d4330ea9-d9d4-4e7c-b9fb-34ee23b83558" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d4330ea9-d9d4-4e7c-b9fb-34ee23b83558_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_d4330ea9-d9d4-4e7c-b9fb-34ee23b83558" xlink:to="loc_dei_EntityDomain_d4330ea9-d9d4-4e7c-b9fb-34ee23b83558_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_bbb0c82d-4601-4457-9b0d-5680f166364f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_d4330ea9-d9d4-4e7c-b9fb-34ee23b83558" xlink:to="loc_dei_EntityDomain_bbb0c82d-4601-4457-9b0d-5680f166364f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_351ca601-a4a8-431c-88ff-b82f389749d6" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_bbb0c82d-4601-4457-9b0d-5680f166364f" xlink:to="loc_swx_CenturiGroupInc.Member_351ca601-a4a8-431c-88ff-b82f389749d6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueRevenuePerformanceObligationDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueRevenuePerformanceObligationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueRevenuePerformanceObligationDetails" xlink:type="extended" id="i5f5116305d564960835c1df74175d5ac_RevenueRevenuePerformanceObligationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_00935335-df2b-4646-9198-685cc9c262ab" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_00935335-df2b-4646-9198-685cc9c262ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_a42b442e-bc53-443e-a777-c6d89a2d7c7a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_a42b442e-bc53-443e-a777-c6d89a2d7c7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_0b1d50dd-0e5e-4875-b483-95915c461943" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_0b1d50dd-0e5e-4875-b483-95915c461943" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_0b1d50dd-0e5e-4875-b483-95915c461943" xlink:to="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_98e24ba1-10a1-4520-97c2-05aaa5191359_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:to="loc_dei_EntityDomain_98e24ba1-10a1-4520-97c2-05aaa5191359_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f9a25278-4c9b-4b01-9849-8df611cbf173" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:to="loc_dei_EntityDomain_f9a25278-4c9b-4b01-9849-8df611cbf173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_ecb38661-fba9-4ff9-bb01-78e83201ba59" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_f9a25278-4c9b-4b01-9849-8df611cbf173" xlink:to="loc_swx_CenturiGroupInc.Member_ecb38661-fba9-4ff9-bb01-78e83201ba59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_253b464e-889c-419e-a564-162b4aca111d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_0b1d50dd-0e5e-4875-b483-95915c461943" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_253b464e-889c-419e-a564-162b4aca111d" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueRevenuePerformanceObligationDetails_1" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueRevenuePerformanceObligationDetails_1"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueRevenuePerformanceObligationDetails_1" xlink:type="extended" id="if0b165b4ffe94aca9643a6338aa0f5a9_RevenueRevenuePerformanceObligationDetails_1">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_00935335-df2b-4646-9198-685cc9c262ab" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_00935335-df2b-4646-9198-685cc9c262ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_a42b442e-bc53-443e-a777-c6d89a2d7c7a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_a42b442e-bc53-443e-a777-c6d89a2d7c7a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_0b1d50dd-0e5e-4875-b483-95915c461943" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_784e6442-5744-4d89-bf57-8f1523af9ce2" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_0b1d50dd-0e5e-4875-b483-95915c461943" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_0b1d50dd-0e5e-4875-b483-95915c461943" xlink:to="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_98e24ba1-10a1-4520-97c2-05aaa5191359_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:to="loc_dei_EntityDomain_98e24ba1-10a1-4520-97c2-05aaa5191359_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_f9a25278-4c9b-4b01-9849-8df611cbf173" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_98e24ba1-10a1-4520-97c2-05aaa5191359" xlink:to="loc_dei_EntityDomain_f9a25278-4c9b-4b01-9849-8df611cbf173" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_ecb38661-fba9-4ff9-bb01-78e83201ba59" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_f9a25278-4c9b-4b01-9849-8df611cbf173" xlink:to="loc_swx_CenturiGroupInc.Member_ecb38661-fba9-4ff9-bb01-78e83201ba59" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueScheduleofGasOperatingRevenueDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueScheduleofGasOperatingRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueScheduleofGasOperatingRevenueDetails" xlink:type="extended" id="i93b7cce8cb1c464bad0c37041943c377_RevenueScheduleofGasOperatingRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_cf750957-736e-48d3-938e-893319fcddf1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b4525421-8d82-4b5e-b651-5c4411be4970" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_cf750957-736e-48d3-938e-893319fcddf1" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b4525421-8d82-4b5e-b651-5c4411be4970" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AlternativeRevenueProgramRevenuesDeferrals_026391d0-c2a6-4af2-82ae-9eb1614cf992" xlink:href="swx-20200630.xsd#swx_AlternativeRevenueProgramRevenuesDeferrals"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_cf750957-736e-48d3-938e-893319fcddf1" xlink:to="loc_swx_AlternativeRevenueProgramRevenuesDeferrals_026391d0-c2a6-4af2-82ae-9eb1614cf992" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherRevenue_03a780e6-b78c-4581-9e70-72c9ee045df4" xlink:href="swx-20200630.xsd#swx_OtherRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_cf750957-736e-48d3-938e-893319fcddf1" xlink:to="loc_swx_OtherRevenue_03a780e6-b78c-4581-9e70-72c9ee045df4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RegulatedOperatingRevenueGas_3cd258ca-9d8f-4493-8cb7-4500a9d14039" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RegulatedOperatingRevenueGas"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_cf750957-736e-48d3-938e-893319fcddf1" xlink:to="loc_us-gaap_RegulatedOperatingRevenueGas_3cd258ca-9d8f-4493-8cb7-4500a9d14039" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_359d6dee-2846-44cd-82ea-f19ea3f57f71" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_cf750957-736e-48d3-938e-893319fcddf1" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_359d6dee-2846-44cd-82ea-f19ea3f57f71" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_c8e3e04a-76a7-4527-9c1d-9a4be0da0941" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_359d6dee-2846-44cd-82ea-f19ea3f57f71" xlink:to="loc_srt_MajorCustomersAxis_c8e3e04a-76a7-4527-9c1d-9a4be0da0941" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_c8e3e04a-76a7-4527-9c1d-9a4be0da0941_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_c8e3e04a-76a7-4527-9c1d-9a4be0da0941" xlink:to="loc_srt_NameOfMajorCustomerDomain_c8e3e04a-76a7-4527-9c1d-9a4be0da0941_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_9a8708f9-fcf4-4290-9be7-1c94c8f0ae8e" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_c8e3e04a-76a7-4527-9c1d-9a4be0da0941" xlink:to="loc_srt_NameOfMajorCustomerDomain_9a8708f9-fcf4-4290-9be7-1c94c8f0ae8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ResidentialMember_11491535-9fe1-42c3-8c0e-de9e95149c8a" xlink:href="swx-20200630.xsd#swx_ResidentialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_9a8708f9-fcf4-4290-9be7-1c94c8f0ae8e" xlink:to="loc_swx_ResidentialMember_11491535-9fe1-42c3-8c0e-de9e95149c8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SmallCommercialMember_b26e0e5d-9425-402f-9746-de5f464402c7" xlink:href="swx-20200630.xsd#swx_SmallCommercialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_9a8708f9-fcf4-4290-9be7-1c94c8f0ae8e" xlink:to="loc_swx_SmallCommercialMember_b26e0e5d-9425-402f-9746-de5f464402c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LargeCommercialMember_336dbe11-cc02-452d-b932-f6bbcba13b71" xlink:href="swx-20200630.xsd#swx_LargeCommercialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_9a8708f9-fcf4-4290-9be7-1c94c8f0ae8e" xlink:to="loc_swx_LargeCommercialMember_336dbe11-cc02-452d-b932-f6bbcba13b71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_IndustrialOrOtherMember_56857e9d-558d-4a34-a602-4c39714611f1" xlink:href="swx-20200630.xsd#swx_IndustrialOrOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_9a8708f9-fcf4-4290-9be7-1c94c8f0ae8e" xlink:to="loc_swx_IndustrialOrOtherMember_56857e9d-558d-4a34-a602-4c39714611f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_TransportationMember_c3a242c9-6014-4865-be55-314cd8773889" xlink:href="swx-20200630.xsd#swx_TransportationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_9a8708f9-fcf4-4290-9be7-1c94c8f0ae8e" xlink:to="loc_swx_TransportationMember_c3a242c9-6014-4865-be55-314cd8773889" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueSummaryofRevenueDisaggregatedbyServiceTypeandContractTypeDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueSummaryofRevenueDisaggregatedbyServiceTypeandContractTypeDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueSummaryofRevenueDisaggregatedbyServiceTypeandContractTypeDetails" xlink:type="extended" id="if4ac534665074b7592f6e536b5b4591e_RevenueSummaryofRevenueDisaggregatedbyServiceTypeandContractTypeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_40844ae1-5888-4f4a-9333-023add411971" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5c18f906-8edb-4b12-be57-101b5ae358bc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_40844ae1-5888-4f4a-9333-023add411971" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5c18f906-8edb-4b12-be57-101b5ae358bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_9fe27de5-2369-4b14-bfd7-310ec5f84f10" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_40844ae1-5888-4f4a-9333-023add411971" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_9fe27de5-2369-4b14-bfd7-310ec5f84f10" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_7cc2e0e3-3db4-44b7-a8ce-e155b8bceb2e" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_9fe27de5-2369-4b14-bfd7-310ec5f84f10" xlink:to="loc_srt_ProductOrServiceAxis_7cc2e0e3-3db4-44b7-a8ce-e155b8bceb2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_7cc2e0e3-3db4-44b7-a8ce-e155b8bceb2e_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_7cc2e0e3-3db4-44b7-a8ce-e155b8bceb2e" xlink:to="loc_srt_ProductsAndServicesDomain_7cc2e0e3-3db4-44b7-a8ce-e155b8bceb2e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_2696baf6-0f0b-4411-89e7-c2bc0329947a" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_7cc2e0e3-3db4-44b7-a8ce-e155b8bceb2e" xlink:to="loc_srt_ProductsAndServicesDomain_2696baf6-0f0b-4411-89e7-c2bc0329947a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ReplacementGasConstructionMember_cf75212e-ca03-45c6-82d6-c3a481106a77" xlink:href="swx-20200630.xsd#swx_ReplacementGasConstructionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_2696baf6-0f0b-4411-89e7-c2bc0329947a" xlink:to="loc_swx_ReplacementGasConstructionMember_cf75212e-ca03-45c6-82d6-c3a481106a77" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_NewGasConstructionMember_dfbb3c16-eb76-4b0d-9707-26934a738465" xlink:href="swx-20200630.xsd#swx_NewGasConstructionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_2696baf6-0f0b-4411-89e7-c2bc0329947a" xlink:to="loc_swx_NewGasConstructionMember_dfbb3c16-eb76-4b0d-9707-26934a738465" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_OtherConstructionMember_e4da6303-e00f-4cae-80cb-ce3ba5db4b91" xlink:href="swx-20200630.xsd#swx_OtherConstructionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_2696baf6-0f0b-4411-89e7-c2bc0329947a" xlink:to="loc_swx_OtherConstructionMember_e4da6303-e00f-4cae-80cb-ce3ba5db4b91" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_aea7530c-455e-4eee-b090-1e4f5f661d97" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerBasisOfPricingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_9fe27de5-2369-4b14-bfd7-310ec5f84f10" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_aea7530c-455e-4eee-b090-1e4f5f661d97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_aea7530c-455e-4eee-b090-1e4f5f661d97_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_aea7530c-455e-4eee-b090-1e4f5f661d97" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_aea7530c-455e-4eee-b090-1e4f5f661d97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_4ca02540-facb-434b-9bbd-e6fe38b77186" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_aea7530c-455e-4eee-b090-1e4f5f661d97" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_4ca02540-facb-434b-9bbd-e6fe38b77186" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_MasterServicesAgreementMember_c8cf9a39-13db-4139-b111-f2ea1751c38a" xlink:href="swx-20200630.xsd#swx_MasterServicesAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_4ca02540-facb-434b-9bbd-e6fe38b77186" xlink:to="loc_swx_MasterServicesAgreementMember_c8cf9a39-13db-4139-b111-f2ea1751c38a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_BidContractMember_f6d11358-7284-4ddb-b635-6ab1c4451d18" xlink:href="swx-20200630.xsd#swx_BidContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_4ca02540-facb-434b-9bbd-e6fe38b77186" xlink:to="loc_swx_BidContractMember_f6d11358-7284-4ddb-b635-6ab1c4451d18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UnitPricedContractsMember_604f03f7-7f03-4468-972a-90d1aa43ae80" xlink:href="swx-20200630.xsd#swx_UnitPricedContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_4ca02540-facb-434b-9bbd-e6fe38b77186" xlink:to="loc_swx_UnitPricedContractsMember_604f03f7-7f03-4468-972a-90d1aa43ae80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedPriceContractMember_86d73e22-5eda-4fae-99ad-fbe4bf62d7a7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FixedPriceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_4ca02540-facb-434b-9bbd-e6fe38b77186" xlink:to="loc_us-gaap_FixedPriceContractMember_86d73e22-5eda-4fae-99ad-fbe4bf62d7a7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeAndMaterialsContractMember_85a93925-8742-40ef-b794-f44ea0e4ee52" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TimeAndMaterialsContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_4ca02540-facb-434b-9bbd-e6fe38b77186" xlink:to="loc_us-gaap_TimeAndMaterialsContractMember_85a93925-8742-40ef-b794-f44ea0e4ee52" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_b9dd3cff-fccc-4a2d-9c47-3b9875e9002f" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_9fe27de5-2369-4b14-bfd7-310ec5f84f10" xlink:to="loc_dei_LegalEntityAxis_b9dd3cff-fccc-4a2d-9c47-3b9875e9002f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b9dd3cff-fccc-4a2d-9c47-3b9875e9002f_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_b9dd3cff-fccc-4a2d-9c47-3b9875e9002f" xlink:to="loc_dei_EntityDomain_b9dd3cff-fccc-4a2d-9c47-3b9875e9002f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_bda96cc3-9b14-4570-a154-e63c00aeebf0" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_b9dd3cff-fccc-4a2d-9c47-3b9875e9002f" xlink:to="loc_dei_EntityDomain_bda96cc3-9b14-4570-a154-e63c00aeebf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_f9c0f366-de35-453f-ab87-e0f4b4458983" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_bda96cc3-9b14-4570-a154-e63c00aeebf0" xlink:to="loc_swx_CenturiGroupInc.Member_f9c0f366-de35-453f-ab87-e0f4b4458983" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueSummaryofInformationaboutReceivablesDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueSummaryofInformationaboutReceivablesDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueSummaryofInformationaboutReceivablesDetails" xlink:type="extended" id="i1c31509220164b358b466af29ee11a3b_RevenueSummaryofInformationaboutReceivablesDetails"/>
  <link:roleRef roleURI="http://www.swgas.com/role/RevenueScheduleofConstructionServicesContractsReceivableDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#RevenueScheduleofConstructionServicesContractsReceivableDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/RevenueScheduleofConstructionServicesContractsReceivableDetails" xlink:type="extended" id="i3db84802ce094f138401d38ab03f076e_RevenueScheduleofConstructionServicesContractsReceivableDetails"/>
  <link:roleRef roleURI="http://www.swgas.com/role/CommonStock" xlink:type="simple" xlink:href="swx-20200630.xsd#CommonStock"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CommonStock" xlink:type="extended" id="icbd2af61abed4d2fb1c518202340f36c_CommonStock"/>
  <link:roleRef roleURI="http://www.swgas.com/role/CommonStockTables" xlink:type="simple" xlink:href="swx-20200630.xsd#CommonStockTables"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CommonStockTables" xlink:type="extended" id="i5bdb7707b58d46fa9234c9c5baa58234_CommonStockTables"/>
  <link:roleRef roleURI="http://www.swgas.com/role/CommonStockDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#CommonStockDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/CommonStockDetails" xlink:type="extended" id="ib22611256118478ea6e896a1afc99b37_CommonStockDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SaleOfStockMaxumumAmountOfStockAllowedToBeOffered_60326708-b929-4b4d-8b3a-5d77ad7aa662" xlink:href="swx-20200630.xsd#swx_SaleOfStockMaxumumAmountOfStockAllowedToBeOffered"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_swx_SaleOfStockMaxumumAmountOfStockAllowedToBeOffered_60326708-b929-4b4d-8b3a-5d77ad7aa662" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_ProceedsFromIssuanceOfCommonStockGross_437a28c9-d743-4088-8862-5372b1df2fd7" xlink:href="swx-20200630.xsd#swx_ProceedsFromIssuanceOfCommonStockGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_swx_ProceedsFromIssuanceOfCommonStockGross_437a28c9-d743-4088-8862-5372b1df2fd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_a2485abe-b6b5-4944-a1b7-0ca17fecb02d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_a2485abe-b6b5-4944-a1b7-0ca17fecb02d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_340826cd-2550-44bf-b548-c1d035544f5c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_340826cd-2550-44bf-b548-c1d035544f5c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_6f506324-5f6d-43d0-b85d-c0a595c23c92" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_6f506324-5f6d-43d0-b85d-c0a595c23c92" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CommonStockWeightedAverageIssuePricePerShare_f197d62e-76cc-4592-8053-ef089fed443c" xlink:href="swx-20200630.xsd#swx_CommonStockWeightedAverageIssuePricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_swx_CommonStockWeightedAverageIssuePricePerShare_f197d62e-76cc-4592-8053-ef089fed443c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SaleOfStockCommonStockAvailableForSale_2dd00dc9-639c-4e20-9874-8f0bfc49d8d9" xlink:href="swx-20200630.xsd#swx_SaleOfStockCommonStockAvailableForSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_swx_SaleOfStockCommonStockAvailableForSale_2dd00dc9-639c-4e20-9874-8f0bfc49d8d9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_d78e0e25-1eee-47ac-a271-42b0dafa584e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_d78e0e25-1eee-47ac-a271-42b0dafa584e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_3d7d1c2c-c038-4fb4-aff3-ad7238c820ed" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_3d7d1c2c-c038-4fb4-aff3-ad7238c820ed" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_0fcdc7eb-9f1e-4afe-9d7b-0c35353ccd9d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_6c7a73d2-80cc-4b17-9352-683ea84cf000" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_0fcdc7eb-9f1e-4afe-9d7b-0c35353ccd9d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_884bf49c-3bea-402d-aba4-8dcfac7280c2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_0fcdc7eb-9f1e-4afe-9d7b-0c35353ccd9d" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_884bf49c-3bea-402d-aba4-8dcfac7280c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_884bf49c-3bea-402d-aba4-8dcfac7280c2_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_884bf49c-3bea-402d-aba4-8dcfac7280c2" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_884bf49c-3bea-402d-aba4-8dcfac7280c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c5920da6-f2ca-4935-968d-275ccf5007ec" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_884bf49c-3bea-402d-aba4-8dcfac7280c2" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c5920da6-f2ca-4935-968d-275ccf5007ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_EquityShelfProgramMember_7ce2dcd4-8732-4556-abe5-36974c305403" xlink:href="swx-20200630.xsd#swx_EquityShelfProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c5920da6-f2ca-4935-968d-275ccf5007ec" xlink:to="loc_swx_EquityShelfProgramMember_7ce2dcd4-8732-4556-abe5-36974c305403" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_be1439ef-7c1a-43c7-8ba3-6729726460f9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_0fcdc7eb-9f1e-4afe-9d7b-0c35353ccd9d" xlink:to="loc_us-gaap_PlanNameAxis_be1439ef-7c1a-43c7-8ba3-6729726460f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_be1439ef-7c1a-43c7-8ba3-6729726460f9_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_be1439ef-7c1a-43c7-8ba3-6729726460f9" xlink:to="loc_us-gaap_PlanNameDomain_be1439ef-7c1a-43c7-8ba3-6729726460f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_153cd843-2000-443a-b8dd-c2c4834f6c85" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_be1439ef-7c1a-43c7-8ba3-6729726460f9" xlink:to="loc_us-gaap_PlanNameDomain_153cd843-2000-443a-b8dd-c2c4834f6c85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_RestrictedStockUnitPlanAndManagementIncentivePlanMember_05538cd4-e971-4447-b1a3-cac0ca04c178" xlink:href="swx-20200630.xsd#swx_RestrictedStockUnitPlanAndManagementIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_153cd843-2000-443a-b8dd-c2c4834f6c85" xlink:to="loc_swx_RestrictedStockUnitPlanAndManagementIncentivePlanMember_05538cd4-e971-4447-b1a3-cac0ca04c178" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DividendReinvestmentAndStockPurchasePlanMember_8118ecbe-eea0-4e89-b1c7-6c9efc80cb0d" xlink:href="swx-20200630.xsd#swx_DividendReinvestmentAndStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_153cd843-2000-443a-b8dd-c2c4834f6c85" xlink:to="loc_swx_DividendReinvestmentAndStockPurchasePlanMember_8118ecbe-eea0-4e89-b1c7-6c9efc80cb0d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/Debt" xlink:type="simple" xlink:href="swx-20200630.xsd#Debt"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/Debt" xlink:type="extended" id="i1ee8c5b61c3a45db97f6c37f0b3674c2_Debt"/>
  <link:roleRef roleURI="http://www.swgas.com/role/DebtTables" xlink:type="simple" xlink:href="swx-20200630.xsd#DebtTables"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/DebtTables" xlink:type="extended" id="i3f63c229ca6c46ce9f26441bd57ab58e_DebtTables"/>
  <link:roleRef roleURI="http://www.swgas.com/role/DebtScheduleofLongTermDebtDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#DebtScheduleofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/DebtScheduleofLongTermDebtDetails" xlink:type="extended" id="icd999e76811e4efe812619f778b5ebc8_DebtScheduleofLongTermDebtDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayable_bd918dc5-7aee-4b3c-9556-744d4db7e13e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_NotesPayable_bd918dc5-7aee-4b3c-9556-744d4db7e13e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesPayableFairValueDisclosure_2725119a-4eee-499e-be59-7e6940094a77" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesPayableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_NotesPayableFairValueDisclosure_2725119a-4eee-499e-be59-7e6940094a77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebtInstrumentUnamortizedDiscountAndDebtIssuanceCosts_3ff6d003-ceb3-417c-a86b-bea28f1476cf" xlink:href="swx-20200630.xsd#swx_DebtInstrumentUnamortizedDiscountAndDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_swx_DebtInstrumentUnamortizedDiscountAndDebtIssuanceCosts_3ff6d003-ceb3-417c-a86b-bea28f1476cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_14242a0d-d643-42fb-aac0-7728b1787adc" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_LineOfCredit_14242a0d-d643-42fb-aac0-7728b1787adc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditFairValueDisclosure_84b382da-e1ce-46be-82fc-a44ec86544e7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LinesOfCreditFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_LinesOfCreditFairValueDisclosure_84b382da-e1ce-46be-82fc-a44ec86544e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebt_68e19192-99ab-415b-8fab-057fa0dd9d98" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnsecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_UnsecuredDebt_68e19192-99ab-415b-8fab-057fa0dd9d98" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_67c2a587-21c4-44b2-b66d-92c0fd5ce249" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_LongTermDebtFairValue_67c2a587-21c4-44b2-b66d-92c0fd5ce249" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_f2e208c4-a7fb-476a-95d3-0931c9cb7bac" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_LongTermDebtCurrent_f2e208c4-a7fb-476a-95d3-0931c9cb7bac" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_c3114c0b-10d0-497d-9bb5-bfcde2097ed9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_c3114c0b-10d0-497d-9bb5-bfcde2097ed9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_ac6b64ec-973f-4422-af06-059188d27904" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_ac6b64ec-973f-4422-af06-059188d27904" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtCurrentAndNoncurrentAbstract_c5fed217-f87e-46f1-8a2d-10dcc36f6ee8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtCurrentAndNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_LongtermDebtCurrentAndNoncurrentAbstract_c5fed217-f87e-46f1-8a2d-10dcc36f6ee8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_45d764a1-5a4b-4bf2-a7d6-e69fb3b49fe5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtCurrentAndNoncurrentAbstract_c5fed217-f87e-46f1-8a2d-10dcc36f6ee8" xlink:to="loc_us-gaap_LongTermDebt_45d764a1-5a4b-4bf2-a7d6-e69fb3b49fe5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_6639b0c5-26b5-4425-885b-d32a97d74dff" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_900f8c83-5092-4507-bfa0-61d4b6eaf466" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebt_2a21629c-a47c-423b-bef2-ce1e897c88e7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_SecuredDebt_2a21629c-a47c-423b-bef2-ce1e897c88e7" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermDebt_40dfdb22-029a-4242-9239-65c7e1fc29e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_OtherLongTermDebt_40dfdb22-029a-4242-9239-65c7e1fc29e3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_bd5fc7b8-25c6-4807-a36b-06c6f629da81" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_bd5fc7b8-25c6-4807-a36b-06c6f629da81" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_fc9e47d1-9b98-4295-8674-1fe9f5402b03" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_4cea84d4-5025-41fe-9ca7-430b114e7da2" xlink:to="loc_us-gaap_DebtInstrumentTable_fc9e47d1-9b98-4295-8674-1fe9f5402b03" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_59766994-78b7-4acd-9685-5d18addf4596" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fc9e47d1-9b98-4295-8674-1fe9f5402b03" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_59766994-78b7-4acd-9685-5d18addf4596" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_59766994-78b7-4acd-9685-5d18addf4596_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_59766994-78b7-4acd-9685-5d18addf4596" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_59766994-78b7-4acd-9685-5d18addf4596_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_59d99fa2-ddb5-45c4-8ebf-df4d575314bd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_59766994-78b7-4acd-9685-5d18addf4596" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_59d99fa2-ddb5-45c4-8ebf-df4d575314bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_5fb0fb0b-6d1e-403b-98d7-0b63cd3647c0" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_59d99fa2-ddb5-45c4-8ebf-df4d575314bd" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_5fb0fb0b-6d1e-403b-98d7-0b63cd3647c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_2cba24f0-5c2b-4571-a601-eb6296330c76" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_59d99fa2-ddb5-45c4-8ebf-df4d575314bd" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_2cba24f0-5c2b-4571-a601-eb6296330c76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_fb6ae8fe-8a08-4f0b-abba-d809892fa9e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_59d99fa2-ddb5-45c4-8ebf-df4d575314bd" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_fb6ae8fe-8a08-4f0b-abba-d809892fa9e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_1b1402cb-8468-43a2-8adf-5c0253e8d395" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fc9e47d1-9b98-4295-8674-1fe9f5402b03" xlink:to="loc_us-gaap_DebtInstrumentAxis_1b1402cb-8468-43a2-8adf-5c0253e8d395" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1b1402cb-8468-43a2-8adf-5c0253e8d395_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1b1402cb-8468-43a2-8adf-5c0253e8d395" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1b1402cb-8468-43a2-8adf-5c0253e8d395_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_22fb53c8-909b-4db7-994d-f961fc9cc212" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1b1402cb-8468-43a2-8adf-5c0253e8d395" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_22fb53c8-909b-4db7-994d-f961fc9cc212" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMember_ee91eb45-36ec-4895-94cd-2a01791c2a1b" xlink:href="swx-20200630.xsd#swx_DebenturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_22fb53c8-909b-4db7-994d-f961fc9cc212" xlink:to="loc_swx_DebenturesMember_ee91eb45-36ec-4895-94cd-2a01791c2a1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_IndustrialDevelopmentRevenueBondsMember_e3b9244f-60e8-482b-8bc0-a535f2e45632" xlink:href="swx-20200630.xsd#swx_IndustrialDevelopmentRevenueBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_22fb53c8-909b-4db7-994d-f961fc9cc212" xlink:to="loc_swx_IndustrialDevelopmentRevenueBondsMember_e3b9244f-60e8-482b-8bc0-a535f2e45632" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_a7e25a2a-42ca-49a4-83f7-f8b203858a06" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fc9e47d1-9b98-4295-8674-1fe9f5402b03" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_a7e25a2a-42ca-49a4-83f7-f8b203858a06" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_a7e25a2a-42ca-49a4-83f7-f8b203858a06_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a7e25a2a-42ca-49a4-83f7-f8b203858a06" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_a7e25a2a-42ca-49a4-83f7-f8b203858a06_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_a7e25a2a-42ca-49a4-83f7-f8b203858a06" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotesFourPointFourFivePercentageDueTwoThousandAndTwentyMember_13601cf9-6708-4712-80b0-7870fb7e358d" xlink:href="swx-20200630.xsd#swx_DebenturesNotesFourPointFourFivePercentageDueTwoThousandAndTwentyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotesFourPointFourFivePercentageDueTwoThousandAndTwentyMember_13601cf9-6708-4712-80b0-7870fb7e358d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotesSixPointOnePercentageDueTwoThousandAndFortyOneMember_2ef7109c-4d92-4b9e-b151-c7abac80ac04" xlink:href="swx-20200630.xsd#swx_DebenturesNotesSixPointOnePercentageDueTwoThousandAndFortyOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotesSixPointOnePercentageDueTwoThousandAndFortyOneMember_2ef7109c-4d92-4b9e-b151-c7abac80ac04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotesThreePointEightSevenFivePercentageDueTwoThousandAndTwentyTwoMember_c167fce3-6162-4c71-8407-2d1372c3e2d4" xlink:href="swx-20200630.xsd#swx_DebenturesNotesThreePointEightSevenFivePercentageDueTwoThousandAndTwentyTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotesThreePointEightSevenFivePercentageDueTwoThousandAndTwentyTwoMember_c167fce3-6162-4c71-8407-2d1372c3e2d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotesFourPointEightSevenFivePercentageDueTwoThousandAndFortyThreeMember_2125fa9a-a5e1-4240-b2d1-efa4e302b47f" xlink:href="swx-20200630.xsd#swx_DebenturesNotesFourPointEightSevenFivePercentageDueTwoThousandAndFortyThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotesFourPointEightSevenFivePercentageDueTwoThousandAndFortyThreeMember_2125fa9a-a5e1-4240-b2d1-efa4e302b47f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotesThreePointEightPercentageDueTwoThousandAndFortySixMember_c78c9446-0345-4e40-8625-4ed4cbe8a338" xlink:href="swx-20200630.xsd#swx_DebenturesNotesThreePointEightPercentageDueTwoThousandAndFortySixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotesThreePointEightPercentageDueTwoThousandAndFortySixMember_c78c9446-0345-4e40-8625-4ed4cbe8a338" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotesThreePointSevenPercentageDueTwoThousandAndTwentyEightMember_8d929347-d67d-4977-bd23-3eda575af56d" xlink:href="swx-20200630.xsd#swx_DebenturesNotesThreePointSevenPercentageDueTwoThousandAndTwentyEightMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotesThreePointSevenPercentageDueTwoThousandAndTwentyEightMember_8d929347-d67d-4977-bd23-3eda575af56d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes415Due2049Member_d0380c1f-d296-4a03-9056-386877e01b19" xlink:href="swx-20200630.xsd#swx_DebenturesNotes415Due2049Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotes415Due2049Member_d0380c1f-d296-4a03-9056-386877e01b19" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes22Due2030Member_8f1c68f0-c8cd-46c3-9022-6b25dd3359e3" xlink:href="swx-20200630.xsd#swx_DebenturesNotes22Due2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesNotes22Due2030Member_8f1c68f0-c8cd-46c3-9022-6b25dd3359e3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesEightPercentageSeriesDueTwoThousandAndTwentySixMember_73e7097d-ee16-4622-a495-792ed9563ffd" xlink:href="swx-20200630.xsd#swx_DebenturesEightPercentageSeriesDueTwoThousandAndTwentySixMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesEightPercentageSeriesDueTwoThousandAndTwentySixMember_73e7097d-ee16-4622-a495-792ed9563ffd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMediumTermNotesSevenPointSevenEightPercentageSeriesDueTwoThousandAndTwentyTwoMember_b9daf3e0-81cc-45c7-a937-2f5f7b354575" xlink:href="swx-20200630.xsd#swx_DebenturesMediumTermNotesSevenPointSevenEightPercentageSeriesDueTwoThousandAndTwentyTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesMediumTermNotesSevenPointSevenEightPercentageSeriesDueTwoThousandAndTwentyTwoMember_b9daf3e0-81cc-45c7-a937-2f5f7b354575" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMediumTermNotesSevenPointNineTwoPercentageSeriesDueTwoThousandAndTwentySevenMember_cc5aff90-55cd-4f23-9370-3d3d5968319b" xlink:href="swx-20200630.xsd#swx_DebenturesMediumTermNotesSevenPointNineTwoPercentageSeriesDueTwoThousandAndTwentySevenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesMediumTermNotesSevenPointNineTwoPercentageSeriesDueTwoThousandAndTwentySevenMember_cc5aff90-55cd-4f23-9370-3d3d5968319b" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMediumTermNotesSixPointSevenSixPercentageSeriesDueTwoThousandAndTwentySevenMember_2982a587-656c-4c0d-980b-a8b8c799c988" xlink:href="swx-20200630.xsd#swx_DebenturesMediumTermNotesSixPointSevenSixPercentageSeriesDueTwoThousandAndTwentySevenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_DebenturesMediumTermNotesSixPointSevenSixPercentageSeriesDueTwoThousandAndTwentySevenMember_2982a587-656c-4c0d-980b-a8b8c799c988" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_RevolvingCreditFacilityAndCommercialPaperMember_75ca0139-6ec6-4627-abd1-330b44f95cc3" xlink:href="swx-20200630.xsd#swx_RevolvingCreditFacilityAndCommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_RevolvingCreditFacilityAndCommercialPaperMember_75ca0139-6ec6-4627-abd1-330b44f95cc3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBondsTaxExemptSeriesADueTwoThousandAndTwentyEightMember_110f479e-3df2-4110-bb1b-824f276ea52f" xlink:href="swx-20200630.xsd#swx_VariableRateBondsTaxExemptSeriesADueTwoThousandAndTwentyEightMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_VariableRateBondsTaxExemptSeriesADueTwoThousandAndTwentyEightMember_110f479e-3df2-4110-bb1b-824f276ea52f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBondsTwoThousandAndThreeSeriesADueTwoThousandAndThirtyEightMember_fb019ed3-cf0d-448e-9f27-bcba93592199" xlink:href="swx-20200630.xsd#swx_VariableRateBondsTwoThousandAndThreeSeriesADueTwoThousandAndThirtyEightMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_VariableRateBondsTwoThousandAndThreeSeriesADueTwoThousandAndThirtyEightMember_fb019ed3-cf0d-448e-9f27-bcba93592199" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBondsTwoThousandAndEightSeriesADueTwoThousandAndThirtyEightMember_3956df0d-bade-457f-b742-e18678dd8040" xlink:href="swx-20200630.xsd#swx_VariableRateBondsTwoThousandAndEightSeriesADueTwoThousandAndThirtyEightMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_VariableRateBondsTwoThousandAndEightSeriesADueTwoThousandAndThirtyEightMember_3956df0d-bade-457f-b742-e18678dd8040" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_VariableRateBondsTwoThousandAndNineSeriesADueTwoThousandAndThirtyNineMember_d62e4d4b-9a7f-4f1a-a50d-760288d2655e" xlink:href="swx-20200630.xsd#swx_VariableRateBondsTwoThousandAndNineSeriesADueTwoThousandAndThirtyNineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_VariableRateBondsTwoThousandAndNineSeriesADueTwoThousandAndThirtyNineMember_d62e4d4b-9a7f-4f1a-a50d-760288d2655e" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiTermLoanFacilityMember_3febb6cd-e831-4727-a82c-2e3859be224a" xlink:href="swx-20200630.xsd#swx_CenturiTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_CenturiTermLoanFacilityMember_3febb6cd-e831-4727-a82c-2e3859be224a" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiOtherDebtObligationsMember_b3239913-8f2a-4c7f-9757-755fbd5ea5e2" xlink:href="swx-20200630.xsd#swx_CenturiOtherDebtObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_e28680e8-ef4b-40b1-a320-5430b55034db" xlink:to="loc_swx_CenturiOtherDebtObligationsMember_b3239913-8f2a-4c7f-9757-755fbd5ea5e2" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_8970e742-6097-40ee-bb6c-29f6ada8e52c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fc9e47d1-9b98-4295-8674-1fe9f5402b03" xlink:to="loc_us-gaap_CreditFacilityAxis_8970e742-6097-40ee-bb6c-29f6ada8e52c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_8970e742-6097-40ee-bb6c-29f6ada8e52c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_8970e742-6097-40ee-bb6c-29f6ada8e52c" xlink:to="loc_us-gaap_CreditFacilityDomain_8970e742-6097-40ee-bb6c-29f6ada8e52c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5560da37-90f3-4d15-a0f3-814cc8039df6" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_8970e742-6097-40ee-bb6c-29f6ada8e52c" xlink:to="loc_us-gaap_CreditFacilityDomain_5560da37-90f3-4d15-a0f3-814cc8039df6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiSecuredRevolvingCreditFacilityMember_0bb10c6d-ea93-4f48-b720-9ad005b41ce8" xlink:href="swx-20200630.xsd#swx_CenturiSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_5560da37-90f3-4d15-a0f3-814cc8039df6" xlink:to="loc_swx_CenturiSecuredRevolvingCreditFacilityMember_0bb10c6d-ea93-4f48-b720-9ad005b41ce8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_e3a2745c-3411-497a-95b4-0858fc9cd710" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fc9e47d1-9b98-4295-8674-1fe9f5402b03" xlink:to="loc_dei_LegalEntityAxis_e3a2745c-3411-497a-95b4-0858fc9cd710" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e3a2745c-3411-497a-95b4-0858fc9cd710_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_e3a2745c-3411-497a-95b4-0858fc9cd710" xlink:to="loc_dei_EntityDomain_e3a2745c-3411-497a-95b4-0858fc9cd710_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_05b7fd0f-bb84-4123-bebd-e6ef8272366e" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_e3a2745c-3411-497a-95b4-0858fc9cd710" xlink:to="loc_dei_EntityDomain_05b7fd0f-bb84-4123-bebd-e6ef8272366e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_5ddd11fb-6687-4367-8ce0-3438151ed27d" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_05b7fd0f-bb84-4123-bebd-e6ef8272366e" xlink:to="loc_swx_SouthwestGasCorporationMember_5ddd11fb-6687-4367-8ce0-3438151ed27d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_f35bd3e9-ff85-44e8-8ea6-38cefdc84f27" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_05b7fd0f-bb84-4123-bebd-e6ef8272366e" xlink:to="loc_swx_CenturiGroupInc.Member_f35bd3e9-ff85-44e8-8ea6-38cefdc84f27" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/DebtAdditionalInformationDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#DebtAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/DebtAdditionalInformationDetails" xlink:type="extended" id="i654bda87136941708002ce17bf2891ca_DebtAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_d260865e-7a8d-46ea-b9bf-5122b1ba5e7e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_d260865e-7a8d-46ea-b9bf-5122b1ba5e7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LineOfCreditFacilityAmountClassifiedAsLongTermDebt_93da5f0b-a594-4ee5-8a3e-68014c8225dd" xlink:href="swx-20200630.xsd#swx_LineOfCreditFacilityAmountClassifiedAsLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_swx_LineOfCreditFacilityAmountClassifiedAsLongTermDebt_93da5f0b-a594-4ee5-8a3e-68014c8225dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_LineOfCreditFacilityWorkingCapitalPurposes_9cface7b-9b4c-4334-a7e7-9db1856d53c2" xlink:href="swx-20200630.xsd#swx_LineOfCreditFacilityWorkingCapitalPurposes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_swx_LineOfCreditFacilityWorkingCapitalPurposes_9cface7b-9b4c-4334-a7e7-9db1856d53c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_b6c03feb-c8e9-4827-8472-f55529bdfe26" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_b6c03feb-c8e9-4827-8472-f55529bdfe26" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_30aa900a-9822-4546-a9dc-e6abbb593a23" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_LongTermDebt_30aa900a-9822-4546-a9dc-e6abbb593a23" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_61261c59-9f76-4134-9f3d-eb9eb97a90e7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_61261c59-9f76-4134-9f3d-eb9eb97a90e7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebtInstrumentCovenantRatioOfFundedDebtToTotalCapitalization_be34b7b9-76f1-4535-8ebb-0e4584e9e119" xlink:href="swx-20200630.xsd#swx_DebtInstrumentCovenantRatioOfFundedDebtToTotalCapitalization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_swx_DebtInstrumentCovenantRatioOfFundedDebtToTotalCapitalization_be34b7b9-76f1-4535-8ebb-0e4584e9e119" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_0cc826dd-e863-4acc-8d0c-71ca8bd297ee" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_LineOfCredit_0cc826dd-e863-4acc-8d0c-71ca8bd297ee" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_0ffb4f66-c586-43fe-bbc6-d6060697b527" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_0ffb4f66-c586-43fe-bbc6-d6060697b527" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_cd07a2cf-99e3-413e-82ce-211b9f49c07b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_cd07a2cf-99e3-413e-82ce-211b9f49c07b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebtInstrumentDiscountRate_e3f117ac-a4a5-43d8-9355-edd4a65c5d1d" xlink:href="swx-20200630.xsd#swx_DebtInstrumentDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_swx_DebtInstrumentDiscountRate_e3f117ac-a4a5-43d8-9355-edd4a65c5d1d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_debedf3e-d431-4a5c-8be0-fdafb1f1040d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_debedf3e-d431-4a5c-8be0-fdafb1f1040d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCollateralAmount_e0157bbd-3123-4855-90b6-d963467cde01" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentCollateralAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_DebtInstrumentCollateralAmount_e0157bbd-3123-4855-90b6-d963467cde01" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_08b1fada-9a0d-4c82-90e8-0a67525e8e49" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_08b1fada-9a0d-4c82-90e8-0a67525e8e49" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_fcae5a3b-9069-49e3-b006-52e6ae56a17e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_ShortTermBorrowings_fcae5a3b-9069-49e3-b006-52e6ae56a17e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebtInstrumentPercentageOfTotalWithInterestRatesReferenceToLIBORAndDueAfter2021_bfce9a88-a032-4f40-9295-5e01a9bfe754" xlink:href="swx-20200630.xsd#swx_DebtInstrumentPercentageOfTotalWithInterestRatesReferenceToLIBORAndDueAfter2021"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_swx_DebtInstrumentPercentageOfTotalWithInterestRatesReferenceToLIBORAndDueAfter2021_bfce9a88-a032-4f40-9295-5e01a9bfe754" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_118b8936-1785-4c8f-8575-3fe0035b64ef" xlink:to="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_839b3164-22c4-44b5-b278-decfcba2c527" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:to="loc_us-gaap_CreditFacilityAxis_839b3164-22c4-44b5-b278-decfcba2c527" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_839b3164-22c4-44b5-b278-decfcba2c527_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_839b3164-22c4-44b5-b278-decfcba2c527" xlink:to="loc_us-gaap_CreditFacilityDomain_839b3164-22c4-44b5-b278-decfcba2c527_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5b409051-50cd-4007-ad4d-f599b30748d2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_839b3164-22c4-44b5-b278-decfcba2c527" xlink:to="loc_us-gaap_CreditFacilityDomain_5b409051-50cd-4007-ad4d-f599b30748d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_A400MillionCreditFacilityMember_214f0769-0ef2-444e-a615-7e6ed38cdec8" xlink:href="swx-20200630.xsd#swx_A400MillionCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_5b409051-50cd-4007-ad4d-f599b30748d2" xlink:to="loc_swx_A400MillionCreditFacilityMember_214f0769-0ef2-444e-a615-7e6ed38cdec8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_A100MillionCreditFacilityMember_c1a271ca-a528-454d-9e18-382902ebfb0d" xlink:href="swx-20200630.xsd#swx_A100MillionCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_5b409051-50cd-4007-ad4d-f599b30748d2" xlink:to="loc_swx_A100MillionCreditFacilityMember_c1a271ca-a528-454d-9e18-382902ebfb0d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_8b04a077-e65e-4649-a96b-964edd931dec" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:to="loc_us-gaap_VariableRateAxis_8b04a077-e65e-4649-a96b-964edd931dec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_8b04a077-e65e-4649-a96b-964edd931dec_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_8b04a077-e65e-4649-a96b-964edd931dec" xlink:to="loc_us-gaap_VariableRateDomain_8b04a077-e65e-4649-a96b-964edd931dec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_608d477c-a3ec-4d77-ac5a-ffe780b64e22" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_8b04a077-e65e-4649-a96b-964edd931dec" xlink:to="loc_us-gaap_VariableRateDomain_608d477c-a3ec-4d77-ac5a-ffe780b64e22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_98130cc1-9d91-4792-a367-f3cfe0144ad7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_608d477c-a3ec-4d77-ac5a-ffe780b64e22" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_98130cc1-9d91-4792-a367-f3cfe0144ad7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_956aa58d-7179-4295-b5e7-e02c0ff3e097" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_608d477c-a3ec-4d77-ac5a-ffe780b64e22" xlink:to="loc_us-gaap_BaseRateMember_956aa58d-7179-4295-b5e7-e02c0ff3e097" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_eaa36ec9-15b0-4e67-a6f0-748ed9665d1b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:to="loc_dei_LegalEntityAxis_eaa36ec9-15b0-4e67-a6f0-748ed9665d1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_eaa36ec9-15b0-4e67-a6f0-748ed9665d1b_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_eaa36ec9-15b0-4e67-a6f0-748ed9665d1b" xlink:to="loc_dei_EntityDomain_eaa36ec9-15b0-4e67-a6f0-748ed9665d1b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_e80cd2e0-7c44-40e7-a943-71c0077cd089" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_eaa36ec9-15b0-4e67-a6f0-748ed9665d1b" xlink:to="loc_dei_EntityDomain_e80cd2e0-7c44-40e7-a943-71c0077cd089" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_233ccc37-4f7a-4bdd-9c39-94ace231d610" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e80cd2e0-7c44-40e7-a943-71c0077cd089" xlink:to="loc_swx_SouthwestGasCorporationMember_233ccc37-4f7a-4bdd-9c39-94ace231d610" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_890f1c6b-7d19-4f63-822f-70c0e1310c97" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_e80cd2e0-7c44-40e7-a943-71c0077cd089" xlink:to="loc_swx_CenturiGroupInc.Member_890f1c6b-7d19-4f63-822f-70c0e1310c97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e706a7bc-0339-4b91-9cfd-c687a04270f9" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:to="loc_srt_RangeAxis_e706a7bc-0339-4b91-9cfd-c687a04270f9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e706a7bc-0339-4b91-9cfd-c687a04270f9_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e706a7bc-0339-4b91-9cfd-c687a04270f9" xlink:to="loc_srt_RangeMember_e706a7bc-0339-4b91-9cfd-c687a04270f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_905359f1-ded9-4dc5-b4ce-22095a404638" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e706a7bc-0339-4b91-9cfd-c687a04270f9" xlink:to="loc_srt_RangeMember_905359f1-ded9-4dc5-b4ce-22095a404638" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c0a825cd-ab87-4527-95a9-b22d8ec86bb0" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_905359f1-ded9-4dc5-b4ce-22095a404638" xlink:to="loc_srt_MinimumMember_c0a825cd-ab87-4527-95a9-b22d8ec86bb0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_2e645876-eab8-4c81-8262-c442bbd92906" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_905359f1-ded9-4dc5-b4ce-22095a404638" xlink:to="loc_srt_MaximumMember_2e645876-eab8-4c81-8262-c442bbd92906" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_74ee659a-c13b-43d8-812b-725a10d9e869" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_74ee659a-c13b-43d8-812b-725a10d9e869" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_74ee659a-c13b-43d8-812b-725a10d9e869_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_74ee659a-c13b-43d8-812b-725a10d9e869" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_74ee659a-c13b-43d8-812b-725a10d9e869_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_74ee659a-c13b-43d8-812b-725a10d9e869" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CommercialPaperProgramMember_764e1c85-a891-43ac-a96c-9d27781c5964" xlink:href="swx-20200630.xsd#swx_CommercialPaperProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:to="loc_swx_CommercialPaperProgramMember_764e1c85-a891-43ac-a96c-9d27781c5964" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotes22Due2030Member_2bbf274f-c9cf-4659-8a72-f9f03a07a410" xlink:href="swx-20200630.xsd#swx_DebenturesNotes22Due2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:to="loc_swx_DebenturesNotes22Due2030Member_2bbf274f-c9cf-4659-8a72-f9f03a07a410" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesNotesFourPointFourFivePercentageDueTwoThousandAndTwentyMember_08b45061-8e59-4225-b8ea-c53e28aeb1c8" xlink:href="swx-20200630.xsd#swx_DebenturesNotesFourPointFourFivePercentageDueTwoThousandAndTwentyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:to="loc_swx_DebenturesNotesFourPointFourFivePercentageDueTwoThousandAndTwentyMember_08b45061-8e59-4225-b8ea-c53e28aeb1c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SecuredRevolvingCreditFacilityTermLoanMember_517fbcfd-9159-441e-87f2-452cc9a2e0f0" xlink:href="swx-20200630.xsd#swx_SecuredRevolvingCreditFacilityTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:to="loc_swx_SecuredRevolvingCreditFacilityTermLoanMember_517fbcfd-9159-441e-87f2-452cc9a2e0f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_cb79b39d-14b9-4a50-8fbe-a6f5a2de1060" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:to="loc_us-gaap_LineOfCreditMember_cb79b39d-14b9-4a50-8fbe-a6f5a2de1060" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiTermLoanFacilityMember_0d2d2ac0-2368-4790-86cf-69b7370bd1f2" xlink:href="swx-20200630.xsd#swx_CenturiTermLoanFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:to="loc_swx_CenturiTermLoanFacilityMember_0d2d2ac0-2368-4790-86cf-69b7370bd1f2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansMember_cd8c8837-66ab-44f6-bdc4-15178e436947" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_23fb8fbe-d812-44cb-858b-a9c7165b8f7c" xlink:to="loc_us-gaap_LoansMember_cd8c8837-66ab-44f6-bdc4-15178e436947" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_e7347244-8a66-4878-9979-e4ad487abd37" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:to="loc_us-gaap_DebtInstrumentAxis_e7347244-8a66-4878-9979-e4ad487abd37" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_e7347244-8a66-4878-9979-e4ad487abd37_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_e7347244-8a66-4878-9979-e4ad487abd37" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_e7347244-8a66-4878-9979-e4ad487abd37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_18e9c4d7-aa76-4732-9604-3516e2bd0004" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_e7347244-8a66-4878-9979-e4ad487abd37" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_18e9c4d7-aa76-4732-9604-3516e2bd0004" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_DebenturesMember_efbf3b5c-6623-4a08-a7bd-4df364c68de7" xlink:href="swx-20200630.xsd#swx_DebenturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_18e9c4d7-aa76-4732-9604-3516e2bd0004" xlink:to="loc_swx_DebenturesMember_efbf3b5c-6623-4a08-a7bd-4df364c68de7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_ef06fff9-8f6a-41e7-9295-9d55fee5da20" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_77a88634-bda7-412d-8b1c-2bda231358d5" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_ef06fff9-8f6a-41e7-9295-9d55fee5da20" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_ef06fff9-8f6a-41e7-9295-9d55fee5da20_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_ef06fff9-8f6a-41e7-9295-9d55fee5da20" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_ef06fff9-8f6a-41e7-9295-9d55fee5da20_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_93d7b422-7414-46e4-b10f-ba21057c3417" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_ef06fff9-8f6a-41e7-9295-9d55fee5da20" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_93d7b422-7414-46e4-b10f-ba21057c3417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_278c5b04-2227-4992-bd71-91928f1493c9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_93d7b422-7414-46e4-b10f-ba21057c3417" xlink:to="loc_us-gaap_SubsequentEventMember_278c5b04-2227-4992-bd71-91928f1493c9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncome" xlink:type="simple" xlink:href="swx-20200630.xsd#OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncome"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncome" xlink:type="extended" id="i8e8522c1108b4ddfa2f3e67a3f3cf279_OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncome"/>
  <link:roleRef roleURI="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeTables" xlink:type="simple" xlink:href="swx-20200630.xsd#OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeTables"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeTables" xlink:type="extended" id="i31095a976f2d4c429797a5cd3edbdc10_OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeTables"/>
  <link:roleRef roleURI="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeRelatedTaxEffectsAllocatedtoOCIDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeRelatedTaxEffectsAllocatedtoOCIDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeRelatedTaxEffectsAllocatedtoOCIDetails" xlink:type="extended" id="ia6ee8d12a34447829e26f5e9f7c7a21e_OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeRelatedTaxEffectsAllocatedtoOCIDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_21ca1810-ed68-4dd6-8156-26e009fa09a4" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_21ca1810-ed68-4dd6-8156-26e009fa09a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_4db85b58-6763-4bcd-a57c-c7f9731cc960" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax_4db85b58-6763-4bcd-a57c-c7f9731cc960" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_989de3cb-1939-411f-b197-26f818a9c2cd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_989de3cb-1939-411f-b197-26f818a9c2cd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_9c6f461f-aec6-4d08-8b3b-1b45ef0e7a06" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_9c6f461f-aec6-4d08-8b3b-1b45ef0e7a06" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodTax_da5ce9ec-e0e3-42ca-ab55-30001870007c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ReclassificationFromAociCurrentPeriodTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodTax_da5ce9ec-e0e3-42ca-ab55-30001870007c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_6c793f73-3ced-4014-8601-18f5fc1e18c8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_6c793f73-3ced-4014-8601-18f5fc1e18c8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_c2475ab5-7d85-48a2-9424-f0dc21cdf0d8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_c2475ab5-7d85-48a2-9424-f0dc21cdf0d8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_09751ae1-c86c-44df-958a-a526e1745af7" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_09751ae1-c86c-44df-958a-a526e1745af7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_7856d7f1-8078-4a91-b663-79f50b94a484" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_7856d7f1-8078-4a91-b663-79f50b94a484" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_e60a87e4-acae-4273-ba8d-f9fb73d5d62a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_e60a87e4-acae-4273-ba8d-f9fb73d5d62a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_14e7ecb6-8258-4117-8dc7-8b27e1fe5f8c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_233c9966-bbd8-434e-a2e2-2e754d2fb1f3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_14e7ecb6-8258-4117-8dc7-8b27e1fe5f8c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_ed50d502-8b01-4f44-8f7d-9d3979bcd243" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_14e7ecb6-8258-4117-8dc7-8b27e1fe5f8c" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_ed50d502-8b01-4f44-8f7d-9d3979bcd243" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_ed50d502-8b01-4f44-8f7d-9d3979bcd243_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ed50d502-8b01-4f44-8f7d-9d3979bcd243" xlink:to="loc_us-gaap_EquityComponentDomain_ed50d502-8b01-4f44-8f7d-9d3979bcd243_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_1c3bfe52-ccf1-4356-af5a-392f8e057659" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_ed50d502-8b01-4f44-8f7d-9d3979bcd243" xlink:to="loc_us-gaap_EquityComponentDomain_1c3bfe52-ccf1-4356-af5a-392f8e057659" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_6a95f54a-89dd-41eb-8bc9-e4c6beeeda98" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1c3bfe52-ccf1-4356-af5a-392f8e057659" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_6a95f54a-89dd-41eb-8bc9-e4c6beeeda98" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_0f964c50-1f13-470d-ac6c-9d97202ff017" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_6a95f54a-89dd-41eb-8bc9-e4c6beeeda98" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_0f964c50-1f13-470d-ac6c-9d97202ff017" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_de4f6f38-0e3f-4969-bc8b-ed293b1e2bf3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_6a95f54a-89dd-41eb-8bc9-e4c6beeeda98" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_de4f6f38-0e3f-4969-bc8b-ed293b1e2bf3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccumulatedDefinedBenefitPlansAdjustmentPriorServiceCostAttributabletoParentMember_781f4ece-ed73-4ee0-893e-c0617ea7315e" xlink:href="swx-20200630.xsd#swx_AccumulatedDefinedBenefitPlansAdjustmentPriorServiceCostAttributabletoParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_6a95f54a-89dd-41eb-8bc9-e4c6beeeda98" xlink:to="loc_swx_AccumulatedDefinedBenefitPlansAdjustmentPriorServiceCostAttributabletoParentMember_781f4ece-ed73-4ee0-893e-c0617ea7315e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccumulatedDefinedBenefitPlansAdjustmentRegulartoryAdjustmentAttributabletoParentMember_d98e77ad-6311-42ac-a2b9-402f1acf8a56" xlink:href="swx-20200630.xsd#swx_AccumulatedDefinedBenefitPlansAdjustmentRegulartoryAdjustmentAttributabletoParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_6a95f54a-89dd-41eb-8bc9-e4c6beeeda98" xlink:to="loc_swx_AccumulatedDefinedBenefitPlansAdjustmentRegulartoryAdjustmentAttributabletoParentMember_d98e77ad-6311-42ac-a2b9-402f1acf8a56" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociDerivativeQualifyingAsHedgeExcludedComponentParentMember_899fd56f-1742-4edf-ad2a-a923c1daa988" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AociDerivativeQualifyingAsHedgeExcludedComponentParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1c3bfe52-ccf1-4356-af5a-392f8e057659" xlink:to="loc_us-gaap_AociDerivativeQualifyingAsHedgeExcludedComponentParentMember_899fd56f-1742-4edf-ad2a-a923c1daa988" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_d5bdab0f-fc54-4f00-8350-234da27dc983" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_1c3bfe52-ccf1-4356-af5a-392f8e057659" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_d5bdab0f-fc54-4f00-8350-234da27dc983" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_61acd251-85da-4df4-aaf3-0569f9b3e0cc" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_14e7ecb6-8258-4117-8dc7-8b27e1fe5f8c" xlink:to="loc_dei_LegalEntityAxis_61acd251-85da-4df4-aaf3-0569f9b3e0cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_61acd251-85da-4df4-aaf3-0569f9b3e0cc_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_61acd251-85da-4df4-aaf3-0569f9b3e0cc" xlink:to="loc_dei_EntityDomain_61acd251-85da-4df4-aaf3-0569f9b3e0cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_ee7ef4e2-ae9b-4f3c-85c1-e1a63bdff3d0" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_61acd251-85da-4df4-aaf3-0569f9b3e0cc" xlink:to="loc_dei_EntityDomain_ee7ef4e2-ae9b-4f3c-85c1-e1a63bdff3d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_89724f8c-8a35-4252-a896-26f3de671759" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_ee7ef4e2-ae9b-4f3c-85c1-e1a63bdff3d0" xlink:to="loc_swx_SouthwestGasCorporationMember_89724f8c-8a35-4252-a896-26f3de671759" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAdditionalInformationDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAdditionalInformationDetails" xlink:type="extended" id="ia4c985084f3c4f15b99f9ac2404dbd3d_OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAdditionalInformationDetails"/>
  <link:roleRef roleURI="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAOCIRollforwardDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAOCIRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAOCIRollforwardDetails" xlink:type="extended" id="i13f6f122623d48afa6e58f1842aaf4cf_OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAOCIRollforwardDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1c162041-4618-4a32-ba70-1dd46d5868e9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1c162041-4618-4a32-ba70-1dd46d5868e9" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestBeforeTax_109b1b5f-8229-4840-b739-496606fe9c42" xlink:href="swx-20200630.xsd#swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestBeforeTax_109b1b5f-8229-4840-b739-496606fe9c42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestTax_72e2d471-7362-41c7-867d-9a408067fc1e" xlink:href="swx-20200630.xsd#swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestTax_72e2d471-7362-41c7-867d-9a408067fc1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_f3795a77-3379-46e2-8b6c-3bf55e743de8" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_f3795a77-3379-46e2-8b6c-3bf55e743de8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityAttributableToParentBeforeTax_0c48a28a-79ac-40c3-b83d-f44053b9a8d2" xlink:href="swx-20200630.xsd#swx_StockholdersEquityAttributableToParentBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_swx_StockholdersEquityAttributableToParentBeforeTax_0c48a28a-79ac-40c3-b83d-f44053b9a8d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityAttributableToParentTax_a316bc33-169c-4739-85ca-7d61c02ab5ca" xlink:href="swx-20200630.xsd#swx_StockholdersEquityAttributableToParentTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_swx_StockholdersEquityAttributableToParentTax_a316bc33-169c-4739-85ca-7d61c02ab5ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_8277b17b-0a6e-422c-b5cb-1d200c73d04c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_StockholdersEquity_8277b17b-0a6e-422c-b5cb-1d200c73d04c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_cca409d6-ee40-48a0-958e-76310181758d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax_cca409d6-ee40-48a0-958e-76310181758d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_db1d622b-289f-43f4-8658-1671069a9cc2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_db1d622b-289f-43f4-8658-1671069a9cc2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_7fd9ae67-55a3-470a-ba6e-802737f3cde9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax_7fd9ae67-55a3-470a-ba6e-802737f3cde9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodTax_ad37105a-a7e4-4d5c-9565-09495aee5867" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ReclassificationFromAociCurrentPeriodTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodTax_ad37105a-a7e4-4d5c-9565-09495aee5867" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_d069b19f-2931-4e47-8bdd-949d46b92915" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_d069b19f-2931-4e47-8bdd-949d46b92915" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_7ea2cd36-8ce4-4c50-9bd5-e1e3caa86def" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_7ea2cd36-8ce4-4c50-9bd5-e1e3caa86def" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_eac839ea-7c41-499f-877d-4b25b3e900cd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_eac839ea-7c41-499f-877d-4b25b3e900cd" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_65216ff2-0b90-4920-9269-a87bbf9a36a9" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_ea334c4c-9f80-4d97-a8a5-a12c2c36b194" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_65216ff2-0b90-4920-9269-a87bbf9a36a9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityAttributableToParentBeforeTax_8c82871c-2812-48cb-834f-2a996703a6f8" xlink:href="swx-20200630.xsd#swx_StockholdersEquityAttributableToParentBeforeTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityAttributableToParentTax_f3373e64-ef90-430d-ab01-3eaac63874b4" xlink:href="swx-20200630.xsd#swx_StockholdersEquityAttributableToParentTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_d30007ec-12b0-4234-b9b4-058d08503427" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestBeforeTax_739a76f4-cffb-4245-a516-af32e62477db" xlink:href="swx-20200630.xsd#swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestBeforeTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestTax_aaf471d2-b3c6-44d8-96ac-cc249ac783b4" xlink:href="swx-20200630.xsd#swx_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestTax"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_c440eda3-7fd6-4bab-85b3-78e284c88ddf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_2abc593d-5f4b-4879-928b-37cd621c4f4d" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1c162041-4618-4a32-ba70-1dd46d5868e9" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_2abc593d-5f4b-4879-928b-37cd621c4f4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_ee91e453-f8b1-4cea-90d8-e37bf42debcd" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_1c162041-4618-4a32-ba70-1dd46d5868e9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_ee91e453-f8b1-4cea-90d8-e37bf42debcd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_1f8ab380-8785-4557-88d6-d503071f332c" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_ee91e453-f8b1-4cea-90d8-e37bf42debcd" xlink:to="loc_dei_LegalEntityAxis_1f8ab380-8785-4557-88d6-d503071f332c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_1f8ab380-8785-4557-88d6-d503071f332c_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1f8ab380-8785-4557-88d6-d503071f332c" xlink:to="loc_dei_EntityDomain_1f8ab380-8785-4557-88d6-d503071f332c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_40ee310e-53df-4250-9788-9db0de86d435" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1f8ab380-8785-4557-88d6-d503071f332c" xlink:to="loc_dei_EntityDomain_40ee310e-53df-4250-9788-9db0de86d435" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_SouthwestGasCorporationMember_6cbaef32-c61d-4878-a06c-30fe2329a5a3" xlink:href="swx-20200630.xsd#swx_SouthwestGasCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_40ee310e-53df-4250-9788-9db0de86d435" xlink:to="loc_swx_SouthwestGasCorporationMember_6cbaef32-c61d-4878-a06c-30fe2329a5a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_cf551acc-61d8-419f-b173-43098cfc6f81" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_ee91e453-f8b1-4cea-90d8-e37bf42debcd" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_cf551acc-61d8-419f-b173-43098cfc6f81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_cf551acc-61d8-419f-b173-43098cfc6f81_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_cf551acc-61d8-419f-b173-43098cfc6f81" xlink:to="loc_us-gaap_EquityComponentDomain_cf551acc-61d8-419f-b173-43098cfc6f81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_18ee21d1-a17c-463e-a842-2a20da279609" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_cf551acc-61d8-419f-b173-43098cfc6f81" xlink:to="loc_us-gaap_EquityComponentDomain_18ee21d1-a17c-463e-a842-2a20da279609" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_fb88d137-e0f9-4d0b-9fc5-e7f7cb2af2e3" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_18ee21d1-a17c-463e-a842-2a20da279609" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_fb88d137-e0f9-4d0b-9fc5-e7f7cb2af2e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_c41328bf-b113-475e-8e9e-0d59c3d0457f" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_fb88d137-e0f9-4d0b-9fc5-e7f7cb2af2e3" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember_c41328bf-b113-475e-8e9e-0d59c3d0457f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_7fab7011-ce08-4b4f-987a-e4b3e933c41b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_fb88d137-e0f9-4d0b-9fc5-e7f7cb2af2e3" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetUnamortizedGainLossMember_7fab7011-ce08-4b4f-987a-e4b3e933c41b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_AccumulatedDefinedBenefitPlansAdjustmentRegulartoryAdjustmentAttributabletoParentMember_a14866ef-a760-4562-bba1-d4200d40d626" xlink:href="swx-20200630.xsd#swx_AccumulatedDefinedBenefitPlansAdjustmentRegulartoryAdjustmentAttributabletoParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_fb88d137-e0f9-4d0b-9fc5-e7f7cb2af2e3" xlink:to="loc_swx_AccumulatedDefinedBenefitPlansAdjustmentRegulartoryAdjustmentAttributabletoParentMember_a14866ef-a760-4562-bba1-d4200d40d626" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociDerivativeQualifyingAsHedgeExcludedComponentParentMember_e6d35ffd-d2a9-42bc-8a23-e6c2a0e0ec85" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AociDerivativeQualifyingAsHedgeExcludedComponentParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_18ee21d1-a17c-463e-a842-2a20da279609" xlink:to="loc_us-gaap_AociDerivativeQualifyingAsHedgeExcludedComponentParentMember_e6d35ffd-d2a9-42bc-8a23-e6c2a0e0ec85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_9db1fd88-ee8c-4e91-ad21-e28b470ef291" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_18ee21d1-a17c-463e-a842-2a20da279609" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_9db1fd88-ee8c-4e91-ad21-e28b470ef291" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_42715afe-aa91-40c3-bad9-10bb69364f5c" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_18ee21d1-a17c-463e-a842-2a20da279609" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_42715afe-aa91-40c3-bad9-10bb69364f5c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAmountsRecognizedBeforeTaxDefinedBenefitPlansDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAmountsRecognizedBeforeTaxDefinedBenefitPlansDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAmountsRecognizedBeforeTaxDefinedBenefitPlansDetails" xlink:type="extended" id="i0c7245e48fce46a58c79469a6e0f2599_OtherComprehensiveIncomeandAccumulatedOtherComprehensiveIncomeAmountsRecognizedBeforeTaxDefinedBenefitPlansDetails"/>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformation" xlink:type="simple" xlink:href="swx-20200630.xsd#SegmentInformation"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformation" xlink:type="extended" id="i95429e9c98f84524a9db19573a964ab0_SegmentInformation"/>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationTables" xlink:type="simple" xlink:href="swx-20200630.xsd#SegmentInformationTables"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationTables" xlink:type="extended" id="i9f0a288cc7924349a580a09a8f97e3d8_SegmentInformationTables"/>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationAccountsReceivableforServicesDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#SegmentInformationAccountsReceivableforServicesDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationAccountsReceivableforServicesDetails" xlink:type="extended" id="i71840b4d311f4376b818a9a6156b9259_SegmentInformationAccountsReceivableforServicesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_6b14d421-bb11-4a48-83bd-703bde24087b" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DueFromRelatedPartiesCurrent_884e89ff-a956-4ad5-9fd6-d88e4c74c234" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DueFromRelatedPartiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_6b14d421-bb11-4a48-83bd-703bde24087b" xlink:to="loc_us-gaap_DueFromRelatedPartiesCurrent_884e89ff-a956-4ad5-9fd6-d88e4c74c234" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_3292ba70-d4d3-49cd-ba5b-29b19a2136bb" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_6b14d421-bb11-4a48-83bd-703bde24087b" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_3292ba70-d4d3-49cd-ba5b-29b19a2136bb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_334e1a8b-a4a9-45c0-99c4-4c65486681f7" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_3292ba70-d4d3-49cd-ba5b-29b19a2136bb" xlink:to="loc_dei_LegalEntityAxis_334e1a8b-a4a9-45c0-99c4-4c65486681f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_334e1a8b-a4a9-45c0-99c4-4c65486681f7_default" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_334e1a8b-a4a9-45c0-99c4-4c65486681f7" xlink:to="loc_dei_EntityDomain_334e1a8b-a4a9-45c0-99c4-4c65486681f7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_d0083d9b-da28-4153-888b-c506d3b1601b" xlink:href="https://xbrl.sec.gov/dei/2019/dei-2019-01-31.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_334e1a8b-a4a9-45c0-99c4-4c65486681f7" xlink:to="loc_dei_EntityDomain_d0083d9b-da28-4153-888b-c506d3b1601b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_CenturiGroupInc.Member_b28e5e40-c148-4e22-a2da-1cd7c8d59fb9" xlink:href="swx-20200630.xsd#swx_CenturiGroupInc.Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_d0083d9b-da28-4153-888b-c506d3b1601b" xlink:to="loc_swx_CenturiGroupInc.Member_b28e5e40-c148-4e22-a2da-1cd7c8d59fb9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationAdditionalInformationDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#SegmentInformationAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationAdditionalInformationDetails" xlink:type="extended" id="i6d639fd31b334970a1ba6e368af690a2_SegmentInformationAdditionalInformationDetails"/>
  <link:roleRef roleURI="http://www.swgas.com/role/SegmentInformationScheduleofReportingInformationDetails" xlink:type="simple" xlink:href="swx-20200630.xsd#SegmentInformationScheduleofReportingInformationDetails"/>
  <link:definitionLink xlink:role="http://www.swgas.com/role/SegmentInformationScheduleofReportingInformationDetails" xlink:type="extended" id="ia5a41f937111480ea77741c5d81b504c_SegmentInformationScheduleofReportingInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_36606f7f-11cd-4a5e-ac9c-95097099d301" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_818fed19-f351-4bf0-9cec-ce77decbcb4a" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_36606f7f-11cd-4a5e-ac9c-95097099d301" xlink:to="loc_us-gaap_Revenues_818fed19-f351-4bf0-9cec-ce77decbcb4a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_00a396dd-0597-4c16-a05d-b7e510446895" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_36606f7f-11cd-4a5e-ac9c-95097099d301" xlink:to="loc_us-gaap_NetIncomeLoss_00a396dd-0597-4c16-a05d-b7e510446895" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_1106dcae-c03f-4aa3-b8da-0eda94f673e1" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_36606f7f-11cd-4a5e-ac9c-95097099d301" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_1106dcae-c03f-4aa3-b8da-0eda94f673e1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_ceb8da30-3643-4cf1-abc8-df9082685f3e" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_1106dcae-c03f-4aa3-b8da-0eda94f673e1" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_ceb8da30-3643-4cf1-abc8-df9082685f3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_ceb8da30-3643-4cf1-abc8-df9082685f3e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ceb8da30-3643-4cf1-abc8-df9082685f3e" xlink:to="loc_us-gaap_SegmentDomain_ceb8da30-3643-4cf1-abc8-df9082685f3e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_13f1f79c-b691-413b-81a2-c57c8a1c27e2" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ceb8da30-3643-4cf1-abc8-df9082685f3e" xlink:to="loc_us-gaap_SegmentDomain_13f1f79c-b691-413b-81a2-c57c8a1c27e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_NaturalGasOperationsMember_a99531b9-4108-4c71-8bfa-6e5f57078f7a" xlink:href="swx-20200630.xsd#swx_NaturalGasOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_13f1f79c-b691-413b-81a2-c57c8a1c27e2" xlink:to="loc_swx_NaturalGasOperationsMember_a99531b9-4108-4c71-8bfa-6e5f57078f7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_swx_UtilityInfrastructureServicesSegmentMember_b740460d-3c29-4f93-87f1-304fe39686aa" xlink:href="swx-20200630.xsd#swx_UtilityInfrastructureServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_13f1f79c-b691-413b-81a2-c57c8a1c27e2" xlink:to="loc_swx_UtilityInfrastructureServicesSegmentMember_b740460d-3c29-4f93-87f1-304fe39686aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_870448c8-f23f-410e-90eb-29842cd3b795" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_1106dcae-c03f-4aa3-b8da-0eda94f673e1" xlink:to="loc_srt_ConsolidationItemsAxis_870448c8-f23f-410e-90eb-29842cd3b795" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_870448c8-f23f-410e-90eb-29842cd3b795_default" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_870448c8-f23f-410e-90eb-29842cd3b795" xlink:to="loc_srt_ConsolidationItemsDomain_870448c8-f23f-410e-90eb-29842cd3b795_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_3cdfefb0-14cf-4379-85f1-a1843cd8542a" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_870448c8-f23f-410e-90eb-29842cd3b795" xlink:to="loc_srt_ConsolidationItemsDomain_3cdfefb0-14cf-4379-85f1-a1843cd8542a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_1514e1f6-e94f-4e20-9e22-0b952e132507" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_3cdfefb0-14cf-4379-85f1-a1843cd8542a" xlink:to="loc_us-gaap_OperatingSegmentsMember_1514e1f6-e94f-4e20-9e22-0b952e132507" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_833aeb2f-a5f8-4b6d-9b62-d7c83ce4c5df" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_3cdfefb0-14cf-4379-85f1-a1843cd8542a" xlink:to="loc_us-gaap_IntersegmentEliminationMember_833aeb2f-a5f8-4b6d-9b62-d7c83ce4c5df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MaterialReconcilingItemsMember_a8b62d37-e47e-4542-bcec-bd2e54734caf" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MaterialReconcilingItemsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_3cdfefb0-14cf-4379-85f1-a1843cd8542a" xlink:to="loc_us-gaap_MaterialReconcilingItemsMember_a8b62d37-e47e-4542-bcec-bd2e54734caf" xlink:type="arc" order="2"/>
  </link:definitionLink>
</link:linkbase>
