This book takes the reader from the basic operating principles of the microwave MESFET and HEMT to the application of device models in modern CAD programmes. In addition to explaining device operation and modelling, the book provides detailed specific algorithms which can be used to efficiently determine the parameters needed to utilize the available device models. Detailed comparisons of MESFET and HEMT performance are presented, and ultimate limitations to these devices are discussed. This book is designed for microwave device and circuit design engineers, GaAs device and MMIC design engineers, MMIC and Hybrid circuit design engineers, and researchers in large signal device modelling.