| U | Uranium |
| U/S | Ultrasonic |
| UART | Universal Asynchronous Receiver/transmitter |
| UBM | Under-bump Metallurgy |
| UCB | Unit Code Browser |
| UCL | Upper Confidence Limit |
| UCL | Upper Control Limit |
| Ueff | Effective Mobility |
| UEL | Upper Explosive Limit |
| UF | Ultra-filtration |
| UFC | Unsaturated Fluorocarbon |
| UFC | Uniform Fire Code |
| UFL | Upper Flammable Limit |
| UHF | Ultra-high Frequency |
| UHP | Ultra-high Purity |
| UHV | Ultra-high Vacuum |
| UI | User Interface |
| UID | User Identification |
| ULA | Uncommitted Logic Array |
| ULK | Ultra Low-k |
| ULPA | Ultra-low Particulate Air |
| ULSI | Ultra Large-scale Integration |
| UPA | Ultraperforming Algorithm |
| UPH | Units Per Hour |
| UPS | Uninterrupted Power Supply |
| UPS | Ultraviolet Photoemission Spectroscopy |
| UPW | Ultrapure Water |
| URD | User Requirement Document |
| URL | Uniform Resource Locator |
| USART | Universal Synchronous/asynchronous Receiver/transmitter |
| USOP | Ultra Small Outline Package |
| USRD | User System Requirement Document |
| Utt | Unattenuated |
| UTV | Unmanned Transport Vehicle |
| UUT | Unit Under Test |
| UV | Ultraviolet |