This paper presents an overview of the latest Gallium Nitride High Electron Mobility Transistor (GaN HEMT) technology. The latest development and challenges of 30 V to 650 V GaN HEMTs are summarized. The evaluation methodology of the GaN HEMT is presented, including static characterization and dynamic characterization. The paper also demonstrates the application of GaN HEMTs developed by Center for High Performance Power Electronics (CHPPE). Various high efficiency high power density circuit prototypes based on GaN HEMTs are presented.