Semiconductor devices used for the detection, generation, amplification, and control of electromagnetic radiation with wavelengths from 30 cm to 1 mm (frequencies from 1 to 300 GHz). Since 1985, the number and variety of microwave semiconductor devices, used for wireless and satellite communication and optoelectronics, have increased as new techniques, materials, and concepts have been developed and applied. Passive microwave devices, such as pn and PIN junctions, Schottky barrier diodes, and varactors, are primarily used for detecting, mixing, modulating, or controlling microwave signals. Step-recovery diodes, transistors, tunnel diodes, and transferred electron devices (TEDs) are active microwave devices that generate power or amplify microwave signals.