| Selnet Ltd | |
| Selteq | |
| Selwyn Electronics Ltd | Kent |
| SEM Consultants Ltd | West Midlands |
| SEM Professional | |
| Semantechs Consulting Ltd | |
| Semarion | |
| Semata Ltd | Bristol |
| Sembee Ltd | Oxfordshire |
| Semefab Ltd | Fife |
| Semetrical | |
| Semiconductor Today | Gloucestershire |
| Sen Corporation Ltd | |
| Senderon | Ards and North Down |
| Sendible | |
| SendOwl | |
| Senior Internet Ltd | Nottinghamshire |
| Senisca Ltd | |
| Senja | |
| Senja Solutions | |
| SENLA | |
| Sens-Tech Ltd | Surrey |
| Sensat | |
| Sensatech Ltd | East Sussex |
| Sensational Systems Ltd | Edinburgh |
| Sense Biodetection Ltd | |
| SENSEcity Ltd | |
| SENSEi Networks | |
| SenseOn Tech Ltd | Greater London |
| Sensi Labs | |
| Sensible Code Company Ltd | |
| Sensible Computing Solutions Ltd | Leicestershire |
| Sensible Internet | Lancashire |
| Sensible PC Solutions | Surrey |
| Senso.cloud | Nottinghamshire |
| Sensor Access Technology Ltd | East Sussex |
| Sensor Studios | Dumfries and Galloway |
| Sensornet Ltd | Hertfordshire |
| Sensory Perception | |
| Sensus3 | Greater London |
| Sente Software Ltd | Surrey |
| Sentient Machines | |
| Sentiment Search Ltd | |
| Sentinel Data Solutions | |
| Sentinel Oncology | |
| Sentinet Computing Ltd | East Sussex |
| Sentio Solutions | |
| Sentiva Ltd | West Yorkshire |
| Sentori | |
| SentrySIS | |