This volume focuses on GaN HEMT, the most promising transistor technology for RF power applications such as 5G communications, space and defense. The contents include accurate small signal models required to predict the RF power performance of RF electronic circuits, large signal modeling of GaN HEMTs, accurate and compact physical models to assist the RF circuit designers to optimize GaN HEMT-based power amplifiers and integrated circuits, among others. The book also covers thermal resistance modeling of GaN HEMTs, charge-based compact models, and surface potential-based models to study the impact of gate leakage current on the RF power performance of GaN HEMTs. This book also deals with the analytical modeling of intrinsic charges and surface potential of GaN HEMTs, physical modeling of charge trapping, neural network-based GaN HEMT models, numerical-based GaN HEMT models, modeling of short channel effects in GaN HEMTs, modeling of parasitic capacitances and resistances, modelingof current collapse and kink effects in HGaN HEMTs, etc. This volume will be a useful to those in industry and academia.