Gallium arsenide (GaAs) is a III–V compound direct-gap semiconductor used for optoelectronics and radio-frequency (RF) devices. One of the biggest selling GaAs devices within today’s compound semiconductor portfolio is the vertical-cavity, surface-emitting laser (VCSEL). It is still the primary material used in edge-emitter lasers (EEL), as well as InP. Another application is RF devices and monolithic-microwave-integrated-circuits (MMICs), including power amplifiers, control products and oscillators. These devices have the advantages of high-speed switching and low noise.