| Siljan Rail AB | Kongsvinger | 2016 |
| Siljans Invest AS | Oslo | 2021 |
| Silkoset Bygg AS | Elverum | 2001 |
| Silo & Maskinmontage I Lidköping AB | Se-531 03 Vinninga | 2012 |
| Silotrust AS | Oslo | 2025 |
| Silsand Maskin AS | Silsand | 1995 |
| Silset Bygg AS | Batnfjordsøra | 2017 |
| Silva Bolig AS | Hamar | 2024 |
| Silver Bygg & Montasje AS | Råde | 2013 |
| Silverdalen Holding AS | Spydeberg | 2022 |
| Silverline | Ee-61709 Tartu Maakond Kambja Vald | 2015 |
| Sim Bygg AS | Oslo | 2020 |
| Sim Elektro AS | Kolbjørnsvik | 2025 |
| Sim Schopf Industriemontagen Und Anlagenbau | At - 9463 Reichenfels | 2015 |
| Simatek | Dk-4180 Sorø | 2019 |
| Simem Spa Nuf | It-37046 Minerbe, Verona | 2015 |
| Simen Arntsen AS | Lavik | 2023 |
| Simen Byberg AS | Kleppe | 2024 |
| Simen Heslien AS | Sylling | 2025 |
| Simen Høgstad Maskinentreprenør AS | Bø I Telemark | 2019 |
| Simen Lindhagen AS | Oslo | 2018 |
| Simen Stølen AS | Hafslo | 2026 |
| Simen Uhlen Holding AS | Lillehammer | 2008 |
| Simenfa Holding AS | Bodø | 2022 |
| Simex Elektro AS | Stavanger | 2016 |
| Simex Rør AS | Stavanger | 2016 |
| Simm AS | Nesttun | 2005 |
| Simo Elektro Entreprenør AS | Larvik | 2025 |
| Simo Teknik AB Nuf | Sparbu | 2025 |
| Simon Hegele Gesellschaft Für Logistikk Und Service MBH | 76131 Karlsruhe | 2007 |
| Simon Power Line Doo | Rs-11050 Beograd | 2016 |
| Simon Torland Holding AS | Fitjar | 2023 |
| Simonsen Entreprenør AS | Straumen | 2025 |
| Simonsen Flislegging AS | Stol | 2020 |
| Simonsen Maskin AS | Misvær | 1991 |
| Simonsen Og Sånt AS | Narvik | 2023 |
| Simonssons Rör Aktiebolag Nuf | Se-780 64 Lima | 2026 |
| Simonstad Byggeri AS | Vegårshei | 2010 |
| Simonstad Drift AS | Selåsvatn | 2017 |
| Simostranda Stav Og Laft AS | Åmot | 2004 |
| Simpel Bygg AS | Oslo | 2024 |
| Simsalabygg AS | Ålesund | 2026 |
| Simtek Ans | Kyrksæterøra | 2008 |
| Simundset & Groeggen Drift AS | Storås | 2023 |
| Simundset & Groeggen Holding AS | Storås | 2023 |
| Sin Bygg Group AS | Furnes | 2022 |
| Sin Projects Ltd | Kent Me8 0Pw England | 2018 |
| Sinabygg AB Nuf | Se-696 92 Askersund | 2026 |
| Sindre Helland AS | Tertnes | 2021 |
| Sindre Holding AS | Alta | 2024 |
| Sindre Nyvoll AS | Alta | 2024 |
| Sindre Stenhaug AS | Brumunddal | 2021 |
| Sindsen Maskin AS | Sande I Vestfold | 2014 |
| Singh Rør AS | Skjetten | 2020 |
| Singro Holding AS | Husnes | 2020 |
| Singstad Holding AS | Ranheim | 2021 |
| Sinneshyttå AS | Tjørhom | 2005 |
| Sinneshyttå Bygg AS | Tjørhom | 1997 |
| Sinotec Nuf | Fosser | 2009 |
| Sins AS | Fetsund | 2016 |
| Sintaksa | Hr-21210 Solin | 2019 |
| Sintec UK Ltd | London Nw10 7Pa | 2023 |
| Sinti Invest AS | Oslo | 2008 |
| Sinus AS | Sandnessjøen | 2002 |
| Sinus Bodø AS | Bodø | 2001 |
| Sinus Brønnøysund AS | Brønnøysund | 1989 |
| Sinus Electro AS | Straumsjøen | 2009 |
| Sinus Elektro AS | Sandnes | 2005 |
| Sinus Holding AS | Sandnes | 2013 |
| Sinus Mosjøen AS | Mosjøen | 2010 |
| Sinus Nesna AS | Nesna | 1985 |
| Sinus Prima AS | Gjerdrum | 2024 |
| Sinusas Bygg & Vedlikehold AS | Saltrød | 2018 |
| Sio Rør AS | Helle | 2019 |
| Sip Hus Lofoten AS | Kabelvåg | 2018 |
| Sip-Tech AS | Oslo | 2004 |
| Sipeurope | 95112 Ivanka Pri Nitre | 2020 |
| Siqveland & Tønnessen AS | Undheim | 2014 |
| Siqveland & Tønnessen Newco AS | Undheim | 2026 |
| Sirdal Betong AS | Tonstad | 2011 |
| Sirdal Betongpumping AS | Kvinesdal | 2015 |
| Sirdal Bygg AS | Tjørhom | 2000 |
| Sirdal El-Installasjon AS | Tonstad | 2019 |
| Sirdal Entreprenør Service AS | Tonstad | 2026 |
| Sirdal Forskaling&Betong AS | Tjørhom | 2019 |
| Sirdal Handlaft AS | Tonstad | 1997 |
| Sirdal Hytter Og Hus AS | Tonstad | 2002 |
| Sirdalsmaleren AS | Tonstad | 2013 |
| Sirdalstjenester AS | Tjørhom | 2020 |
| Sirelle AS | Kjørsvikbugen | 2008 |
| Siriel AS | Bogøy | 2018 |
| Siring AS | Arendal | 2006 |
| Sirius Business Group | Dk-2960 Rungsted Kyst | 2009 |
| Sirius Skipper & Yachting Services AS | Svolvær | 2017 |
| Sirkulær Ressurssentral AS | Oslo | 2021 |
| Siro Bygg AS | Odda | 2016 |
| Sirumi Drift AS | Mo I Rana | 2018 |
| Sirør AS | Oslo | 2025 |
| Sisema AS | Garnes | 2014 |
| Sisjord AS | Gvarv | 2023 |