| SICOFI | Signalling Codec Filter |
| SIDP | Sputter ion depth profiling |
| SiGe | Silicon Germanium |
| SiH4 | Silane |
| SIL | Systems Integration Lab (was ATF) |
| SIMO | Single input, multi output |
| SIMOX | Separation by implantation of oxygen |
| SIMS | Secondary Ion Mass Spectroscopy |
| SIO | Serial Input Output |
| SIOA | Surface Induced Optical Anisotropy |
| SIP | Single Inline Package; Session Initiation Protocol |
| SIPO | Serial In Parallel output |
| SIR | Surface Insulation Resistance |
| SIRIJ | Semiconductor Industry Research Institute of Japan |
| SISFET | Semiconductor-Insulator-Semiconductor FET |
| SISO | Single input, single output; Serial in serial out |
| SIV | Sensors in vacuum |
| SL | Specification limit; Super lattice |
| SLAC | Subscriber Line Audio processing interface |
| SLAM | Scanning laser acoustic microscopy; Single layer alumina metallization |
| SLC | Surface laminar circuit |
| SLD | Strong Lattice Deformation |
| SLEED | Spin-Polarized Low Energy Electron Diffraction (aka SPLEED) |
| SLIC | Standard-function Linear Integrated Circuit; Subscriber Line Interface Circuit |
| SLICOFI | Subscriber Line Interface Circuit and Signaling Codec Filter |
| SLIP | Single Line Internet Protocol |
| SLM | Spatial Light Modulator |
| SLOC | Source lines of code |
| SLPSS | Semiconductor Laser Pumped Solid State (laser source) |
| SLR | Small Lattice Relaxation |
| SLS | Strained Layer SL |
| SLSI | Super large scale integration |
| Sm | Samarium |
| SM | Stress migration; Surface mount |
| SMA | Shape Memory Alloy; Surface mount assembly |
| SMB | Single-mask bumping |
| SMC | Surface-mounted components |
| SMD | Surface Mount Devices |
| SME | Subject matter expert; Software maintenance engineer |
| SMEMA | Surface Mount Equipment Manufacturers Association |
| SMG | Screen management guide |
| SMID | Single Instruction Multiple Data |
| SMIF | Standard mechanical interface |
| SMIL | Synchronized Multi-media Integration Language |
| SMOBC | Solder mask over bare copper |
| SMPM | SECS message protocol machine |
| SMPTE | Society of Motion Picture and Television Engineers |
| SMR | Semiconductor mask representation |
| SMS | SECS message service; Short Messaging Service |
| SMSC | Short Message Switching Center |
| SMT | Surface Mount Technology |
| SMTA | Surface Mount Technology Association |
| SMTP | Simple Mail Transfer Protocol |
| SMTS | Strategic Material Transport System |
| Sn | Tin |
| S/N | Signal-to-noise; Serial number |
| SNA | Systems Network Architecture |
| SNAP | Selective Niobium Anodization Process |
