| Seomark | A Coruña |
| SeoPosicion | Granada |
| SEOPRO Marketing Online, S.L. | |
| SEOSEM | Alicante |
| Sepmag | |
| Sepmag Systems, S.L. | Barcelona |
| Sepomo, S.L. | Madrid |
| Sepsia Therapeutics | |
| Seqera Labs, S.L. | Barcelona |
| Sequentia Biotech, S.L. | Barcelona |
| Serabiotics | |
| Seratel Technology, S.A.L. | Madrid |
| Sercaman, S.L. | Toledo |
| Sercom Cloud & Support | Valencia |
| Serednet Works | Ourense |
| SEREM | Madrid |
| Serendeepia Research, S.L. | |
| Seresco | Asturias |
| Serialnet, Networking i Software Lliure, S.L. | Barcelona |
| Serikat Consultoria e Informatica, S.A. | Biscay |
| Seringe, S.A. | Madrid |
| Serman | Madrid |
| Sermes | |
| SERSEO | Cantabria |
| Sertecnet Valencia | Valencia |
| Serveis d'Internet Javajan | Barcelona |
| Servicio Móvil | A Coruña |
| Servicios de Hosting en Internet, S.A. | Madrid |
| Servicios Especiales de Codificación, S.A. | Biscay |
| Servicios Informáticos El Muelle, S.L. | A Coruña |
| Servicios Técnicos Interactivos de Networking y Protección de Datos, S.L. | Madrid |
| Serviempresa | Valencia |
| ServiHosting Networks, S.L. | Alicante |
| ServiNetwork, S.C.P. | Barcelona |
| Serviport Andalucía, S.A. | Sevilla |
| ServiTux | Alicante |
| Setecem | Barcelona |
| Setting Consultoria | Barcelona |
| SetUp Oneline, S.L. | |
| Several | |
| Sewan | Madrid |
| SG Multimèdia | Barcelona |
| Shakers | |
| Shakers | |
| Sheetgo | Valencia |
| Ship2B Foundation | Barcelona |
| Shopery | Barcelona |
| SHS Consultores | Sevilla |
| Sicaman Nuevas Tecnologías, S.L. | Ciudad Real |
| SicaSoft | Madrid |