| Sierra West Floor Covering INC | Amando Nicolas Ruiz Rojas | — | (925) 956 3026 | Other | Concord · Contra Costa County | — | — |
| Sierra-pacific Construction | Larry Earl Hansohn | — | (925) 260 3362 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| Sigalas Flooring INC | Garfias Cristian Ponce | jorge@sigalasflooring.com | (925) 664 5608 | Other | Pittsburg · Contra Costa County | — | — |
| Signature Finish | Signature Finish | — | (925) 436 7144 | Windows, patio, painters | Martinez · Contra Costa County | — | — |
| Silicon Valley Elevators | Luis Guillermo Vallejos | — | (415) 850 7307 | Other | Pleasant Hill · Contra Costa County | — | — |
| Silva Construction | Michael Joseph Jr Silva | — | (925) 980 6037 | GC, remodel, ADU | Brentwood · Contra Costa County | — | — |
| Silva Contractors INC | Geicyler Henrique Silva | sales@silva-contractors.com | (510) 275 3329 | Other | Pinole · Contra Costa County | — | — |
| Silva Enterprises General Contractor | Silva Francisco | — | (925) 783 3414 | GC, remodel, ADU | Oakley · Contra Costa County | — | — |
| Silver Painting | Silver Painting | shainon@site123-gal-editor-b.com | (510) 691 9220 | Windows, patio, painters | San Pablo · Contra Costa County | — | — |
| Silverado Valley Electric | Hector Daniel Jr Tovar | — | (925) 969 1111 | Electricians | Clayton · Contra Costa County | — | — |
| Silverwood Construction | Jose Ramon Diaz | — | (510) 381 7270 | GC, remodel, ADU | Lafayette · Contra Costa County | — | — |
| Simcon Company | Jack Lee Simmons | — | (925) 640 2267 | GC, remodel, ADU | Discovery Bay · Contra Costa County | — | — |
| Simonds Lois DBA Gardening By Natures Design | Lois Renee Simonds | — | (510) 232 8360 | Windows, patio, painters | Richmond · Contra Costa County | — | — |
| Simple Pavers INC | Vladimir A Kaplun | — | (925) 890 6606 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| Simplisafe | Simplisafe | customer-support@simplisafe.co.uk | — | Alarm and generators | Concord · Contra Costa County | — | — |
| Simply Integrated | Simply Integrated | — | (925) 550 5037 | GC, remodel, ADU | Discovery Bay · Contra Costa County | — | — |
| Sinclair Builder | Sinclair Builder | — | (925) 360 6152 | GC, remodel, ADU | Walnut Creek · Contra Costa County | — | — |
| Sinclair Construction Co INC | Jamison Daniel Sinclair | — | (925) 672 4401 | GC, remodel, ADU | Concord · Contra Costa County | — | — |
| Singelstad Construction INC | Peter Martin Singelstad | — | (925) 999 0854 | GC, remodel, ADU | Orinda · Contra Costa County | — | — |
| Singh Security INC | Singh Bhupinder | — | (510) 386 6059 | Electricians | Danville · Contra Costa County | — | — |
| Sino Home Deco | Sino Home Deco | — | (510) 673 7032 | GC, remodel, ADU | Pittsburg · Contra Costa County | — | — |
| Sinoscan Construction Co INC | Su Liang | — | (510) 524 8938 | GC, remodel, ADU | El Cerrito · Contra Costa County | — | — |
| Sitecare Landscape Maintenance INC | Grant Boyd Hatfield | — | (510) 843 0409 | Windows, patio, painters | Richmond · Contra Costa County | — | — |
| Sitewatch Technology – Mobile Surveillance Tower | Sitewatch Technology – Mobile Surveillance Tower | — | (800) 200-0666 | Alarm and generators | Chatsworth · Contra Costa County | — | — |
| Siteworks Construction INC | Mark Leo Turrin | — | (925) 284 1437 | Other | Lafayette · Contra Costa County | — | — |
| Siteworks Landscape INC | Grant Boyd Hatfield | — | (510) 843 0409 | Windows, patio, painters | Richmond · Contra Costa County | — | — |
| Sizemore & Son | Thomas Wayman Sizemore | — | (925) 584 4560 | Other | Oakley · Contra Costa County | — | — |
| Sjd Landscaping | Raymundo Alvarado Ramirez | — | (925) 206 1255 | Windows, patio, painters | Antioch · Contra Costa County | — | — |
| Skc Tile & Stone | Skc Tile & Stone | — | (925) 639 1011 | Other | Oakley · Contra Costa County | — | — |
| Skim N Dip LLC | Nicholas Donald Eisenbart | — | (925) 348 5609 | Pool | Concord · Contra Costa County | — | — |
| Skinner Painting And Decorating | Skinner Painting And Decorating | — | (925) 518 9169 | Windows, patio, painters | Walnut Creek · Contra Costa County | — | — |
| Skl Electric | Sklyar Yuri | — | (925) 395 3671 | Electricians | Concord · Contra Costa County | — | — |
| Skuba Construction Services INC | David James Jr Skuba | — | (925) 689 5900 | GC, remodel, ADU | Clayton · Contra Costa County | — | — |
| Sky Moon Holdings Incorporated | Shawn Christian Wallace | — | (707) 290 3112 | HVAC | Rodeo · Contra Costa County | — | — |
| Skylandscape LLC | Skyler Herbert Brady | — | (925) 400 8868 | Windows, patio, painters | San Ramon · Contra Costa County | — | — |
| Skyline Capital Builders LLC | David Anthony Hayes | — | (415) 908 1020 | GC, remodel, ADU | Walnut Creek · Contra Costa County | — | — |
| Skyline Garage Doors | Mahdy Lafy Ibrahim | — | (925) 705 0693 | Other | Antioch · Contra Costa County | — | — |
| Skyline Painting | Skyline Painting | — | (415) 637 2086 | Windows, patio, painters | Bay Point · Contra Costa County | — | — |
| Skyroof INC | Myung A Han | — | (925) 876 1011 | Other roofers | Walnut Creek · Contra Costa County | — | — |
| Skytown Mechanical | Skytown Mechanical | info@skytownmechanical.com | (510) 508 2349 | HVAC | El Cerrito · Contra Costa County | — | — |