| Slipe-Service AS | Manufacturing | 2015 |
| Slottet Eiendom AS | Real estate | 2004 |
| Smart Bilservice AS | Other services | 2006 |
| Smil Kardiologi AS | Health & social care | 2025 |
| Smilefjeset Tannklinikk AS | Health & social care | 2012 |
| Smith-Meyer Management Group AS | Real estate | 2016 |
| Småtroll Harstad AS | Education | 2015 |
| Snekkermartin AS | Construction | 2021 |
| Snekkermartin Holding AS | Agriculture & fishing | 2011 |
| Sol Noctis Holding AS | | 2021 |
| Solheim Brygga AS | Arts & recreation | 2014 |
| Solknausen Harstad AS | Professional & scientific | 2013 |
| Sollia Hund Og Hest Da | Wholesale & retail | 2005 |
| Sollifjellet Alpinsenter SA | Arts & recreation | 1985 |
| Sommerseth Holding AS | Professional & scientific | 2009 |
| Soniro AS | Information & communication | 2015 |
| Sos Byggdrift AS | Construction | 2025 |
| Sp-Maskin AS | Construction | 2003 |
| Spaspa by Mikkelborg AS | Other services | 2005 |
| Spaspa by Mikkelborg Avd. Kanebogen | Other services | 2014 |
| Specon Miljø AS | Water & waste | 2005 |
| Spesialistklinikken AS | Health & social care | 2016 |
| Spesialistklinikken Stein Dragland AS | Health & social care | 2013 |
| Spire Invest AS | | 2015 |
| Sport 1 Harstad AS | Wholesale & retail | 2021 |
| Sshc AS | Education | 2008 |
| ST Olavs Gate 182 AS | Real estate | 2022 |
| St-Eiendom AS | Real estate | 2004 |
| St-Holding AS | Construction | 2008 |
| St-Klimaservice AS | Construction | 2009 |
| St-Klimateknikk AS | Construction | 1991 |
| Stairways to Heaven AS | Wholesale & retail | 2016 |
| Stalheim Holding AS | Professional & scientific | 2016 |
| Stall Nordavind AS | Agriculture & fishing | 2026 |
| Stammen Bjarkøy AS | Arts & recreation | 2025 |
| Stangnes Bilskade AS | Other services | 2022 |
| Stangnes Invest AS | Hospitality | 2005 |
| Stangnes Rorbuer AS | Hospitality | 2017 |
| Stangnes Utvikling AS | Real estate | 2017 |
| Stangneshallen AS | Arts & recreation | 1987 |
| Stangnesterminalen 15 AS | Other services | 2012 |
| Stangnesterminalen 3 AS | Real estate | 2008 |
| Stanjo Holding AS | | 2020 |
| Ste-Mor Invest AS | Financial services | 2006 |
| Steinbakken Invest AS | Professional & scientific | 2012 |
| Steinbergneset Eiendom AS | Real estate | 1996 |
| Steirobygget AS | Real estate | 1970 |
| Stene AS | Manufacturing | 1997 |
| Stene Eiendom Harstad AS | Real estate | 2008 |
| Sterk Cooling AS | Professional & scientific | 2019 |
| Stigma Salg Og Tjenester AS | Wholesale & retail | 2008 |
| Stihaug Villsau Da | Manufacturing | 2004 |
| Stine Thoresen AS | Other services | 2023 |
| Stips AS | Professional & scientific | 2019 |
| Stokkan Lys Nord AS | Wholesale & retail | 1996 |
| Stonestream Holding AS | | 2021 |
| Stopp Eiendom AS | Real estate | 2004 |
| Storbakkveien 3 AS | Real estate | 2025 |
| Storgata 1 Harstad AS | Other services | 2012 |
| Storgata 11 Harstad AS | Real estate | 2008 |
| Storgata 3 AS | Real estate | 1996 |
| Storgata 3 Eiendom AS | Real estate | 2019 |
| Storgata 33 AS | Real estate | 2008 |
| Storgata 44 Tromsø AS | Real estate | 2013 |
| Storgata 5 Harstad AS | Real estate | 2003 |
| Storgatens Glassmagasin AS | Wholesale & retail | 1990 |
| Stormglass AS | Construction | 2022 |
| Stormo Multiservice AS | Real estate | 2019 |
| Storvig Design AS | Professional & scientific | 2015 |
| Storåkeren 15 AS | Wholesale & retail | 2015 |
| Storåkeren 9 AS | Real estate | 2021 |
| Strandgata 1 Eiendom AS | Real estate | 2018 |
| Strandgata 14B AS | Real estate | 2015 |
| Strandgata 15 AS | Real estate | 2020 |
| Strandgata 9 Harstad AS | Real estate | 2012 |
| Strandgt 17 AS | Real estate | 1994 |
| Strandveien 13 AS | Real estate | 2013 |
| Strandåkeren 15 Harstad AS | Real estate | 2010 |
| Straumsnes Eiendom AS | Real estate | 2017 |
| Straumsnes Holding AS | Construction | 2017 |
| Studio Kaos AS | Information & communication | 2023 |
| Studio V AS | Other services | 2022 |
| Styling Your Home AS | Professional & scientific | 2023 |
| Støperiet Harstad AS | Real estate | 2018 |
| Støperigården Eiendom AS | Real estate | 2010 |
| Sulland Bilskade Harstad AS | Other services | 2001 |
| Sulland Harstad AS | Other services | 1987 |
| Sundsvold Holding AS | | 2013 |
| Supreme Bilfoliering AS | Other services | 2020 |
| Surface Protection Technology AS | Manufacturing | 2022 |
| Sushi Plus AS | Hospitality | 2024 |
| Sushi Point Harstad AS | Hospitality | 2017 |
| Svartåsen Eiendom Harstad AS | Real estate | 2023 |
| Svenn-Inge Hjelmsø AS | Wholesale & retail | 2007 |
| Svenn-Inge Hjelmsø Dagligvare AS | Wholesale & retail | 2023 |
| Sverre Haukebøe Holding AS | | 2025 |
| Svma AS | Information & communication | 2022 |
| SW Eiendomsutvikling AS | Real estate | 2019 |
| Systeminvest AS | Real estate | 1984 |
| Solstad Begravelsesbyrå AS | Other services | 1987 |