Three two-hour sessions. There are a number of semiconductor technologies being used for power amplifier design. This course introduces students to the GaN transistor, its properties, various structures, discrete and MMIC devices. The properties of GaN will be presented showing the advantage of these devices over other materials for power amplifier applications. Material will be presented on GaN HEMT transistors, geometries, semiconductor processes and structures with associated breakdown voltages, power capability, gain, efficiency, and frequency performance. Guidelines for reliable operation will be presented considering device junction temperature including thermal management techniques. MMIC matching and biasing elements will be shown. The nonlinear models of GaN HEMT devices necessary for the Computer Aided Design ( CAD) of power amplifiers will be presented. Design considerations for both constant amplitude envelope signals as well as the non-constant amplitude envelope signals will be presented. Design procedures will be shown for various GaN PA examples including different classes of operation as well as the popular Doherty PA.