| SoftSign MultiMedia Group | East Flanders |
| Software4U | |
| SOLiTHOR | |
| Solvay Business School of Economics & Management | |
| Sonaca S.A. | |
| Sonal N.V. | Antwerp |
| Sonitron N.V. | East Flanders |
| SOTRAD S.P.R.L. | Walloon Brabant |
| Space Applications Services S.A./N.V. | Flemish Brabant |
| Space Hubs Network | |
| Spacebel | Liège |
| Spacewell International | Antwerp |
| Spatie | |
| Spectralys Biotech S.P.R.L. | |
| Spectricity N.V. | |
| SpeechWare | Brussels-Capital |
| Speed.be | Namur |
| Spencer | |
| Spica Therapeutics | |
| SPIE Belgium ICS | Walloon Brabant |
| Spikes N.V. | Antwerp |
| SportUp | East Flanders |
| Spott | |
| srtt.be | Liège |
| StackGuardian B.V. | |
| StarApps | |
| Starring Jane | |
| Start it Accelerate | |
| Startup Europe | Brussels-Capital |
| Startup Europe News | |
| Startup Europe Partnership | Brussels-Capital |
| Startup Factory | |
| Startup Scaleup | Brussels-Capital |
| Startup.Flanders | |
| Startups.be | Brussels-Capital |
| Stellar Data Recovery B.V. | Brussels-Capital |
| Stellar Development | |
| Step ITS | Walloon Brabant |
| StoryMe | |
| Straffe Sites | |
| STRATENET S.P.R.L. | Namur |
| Stream Software | |
| StriveCloud | |
| Stuart | Antwerp |
| Students for Innovation & Cooperation | |
| Studio Emma | |
| Studio Webvision | |
| Studio2.0 | Namur |
| Studiopointcarré | Liège |
| Summ.link | |