Microwave transistors are useful as small-signal amplifiers to 6 GHz and power amplifiers to 4 GHz. Nearly all microwave transistors are of the silicon planar type. Power transistors use three types of geometries--interdigitated, overlay, and mesh--while small-signal transistors use interdigitated only. The general theory of the frequency response of transistors is reviewed, including active and inactive elements. A condensed description of the design and processing steps for a silicon microwave transistor is given. A final section deals with the types of high-frequency measurements used in the design and analysis of transistors.