| ALS | Advanced light source; Advanced low-power Schottky |
| ALT | Alternating |
| ALU | Arithmetic logic unit |
| ALVT | Advanced low voltage technology |
| Am | Americium |
| AM | Amplitude modulation; Ante meridiem (before noon) |
| AMC | Airborne molecular contamination |
| AMD | Alpha micro devices |
| AMDM | ATM Multiplexer/DeMultiplexer (QSI) |
| AMH | Automated material handling |
| AMHS | AMH Systems |
| AMI | Alternate Mark Inverse Code |
| AML | Automatic model linking |
| AMLCD | Active Matrix LCD |
| AMM | Acoustic Mismatch Model; Analog Multimeter |
| Amp | Amplifier |
| AMPS | Advanced Mobile Phone System |
| AMRAAM | Advanced Medium Range Air-to-Air Missile |
| AMT | Advanced manufacturing technology |
| AMU | Atomic mass unit |
| AND | Logic term - AND |
| ANN | Artificial Neural Network |
| ANOVA | Analysis Of Variance |
| ANPA | American Newspaper Publishers Association |
| ANSI | American National Standards Institute |
| AOI | Automatic Optical Inspection; And-Or-Invert |
| AOQL | Average Outgoing Quality Level |
| AOV | Air-Operated Valve |
| AP | Adhesion Promoter |
| APA | Advanced Performance Algorithm |
| APB | Anti Phase Boundary |
| APC | Advanced Process Control; Automatic Phase Control |
| APCD | Add-on Pollution Control Devices |
| APCFI | Advanced Process Control Framework Initiative |
| APCVD | Atmospheric Pressure Chemical Vapor Deposition |
| APD | Avalanche Photo Diode |
| APEC | Advanced Process Equipment Control |
| API | Application Programming Interface; Atmospheric Pressure Ionization |
| APIMS | Atmospheric Pressure Ionization Mass Spectroscopy |
| APM | Atmospheric Passivation Module; Acoustic Plate Mode |
| APS | American Physical Society |
| APT | Advanced Probe Technology; Automatically Programmed Tools |
| APVD | Alcatel Plasma Vapor Deposition (Alcatel-France) |
| APW | Augmented Plane Wave |
| AQI | ACCESS Query Interface |
| AQL | Acceptance Quality Level: Acceptable Quality Level |
| AQTX | Aquatic Toxicity |
| Ar | Argon |
| AR | Aspect Ratio |
| ARAMS | Automated Reliability, Availability, and Maintainability Standard |
| ARC | Antireflective Coating |
| ARCOFI | Audio Ringing Codec Filter |
| ARDE | Aspect-Ratio-Dependent Etching |
| ARIB | Association of Radio Industries and Businesses |
| ARIMA | Auto Regressive Moving Average with Integration |
| ARINC | Aeronautical Radio Incorporated |
| ARO | After Receipt of Order |
| ARPA | Advanced Research Projects Agency (formerly DARPA) |
| ARPES | Angular Resolved Photo Electron Spectroscopy |
