- Oak Frequency Control
- Oak Technology
- Oasis Semiconductor, Inc.
- ODU
- OhmCraft, Inc.
- Ohmite
- Okaya Electric
- Oki Semiconductor
- OKW Enclosures, Inc.
- Omega Power Systems
- Omega Shielding Products, Inc.
- Omnirel Corp.
- Omron Electronics
- OnSpec Oscillators
- Op Amp Labs, Inc.
- Optek Technology, Inc.
- OPTi, Inc.
- OPT Industries
- Opto 22
- Opto Diode Corp.
- Optotek Ltd.
- Orbit Semiconductor
- Oryx Power Products
- Oscillatek
- Otto Engineering
- Oxford Semiconductor
