Power electronic device plays a critical role in the generation, storage, conversion, and distribution of the electrical energy. Because the global energy shortage is, from time to time, an international crisis and economic threat, people have the demand on more advanced power semiconductor to provide efficient control of the power system. In the past several decades, Si has been widely used in power electronics, ranging from several volts to thousand voltage operations. It has the advantage of low cost and high reliability. However, the development of Si power electronics has reached its theoretical limit. The semiconductor power industry has developed very efficient topologies of power circuits and approaches for power management by fully utilizing the electrical and material characteristics of Si power devices. To further bring up the performance of power systems, alternative semiconductor materials with higher reliability at high switching speeds, current levels, and breakdown field are explored. In the past several years, with the mature nitride semiconductor in optical and electrical devices, gallium nitride (GaN) is set to displace Si power devices as III-nitride compound materials with better power handling and higher switching speed. The conversion efficiency is increased, allowing the implementation of essential future “cleantech” innovations, where power, weight, and volumetric efficiency are the key requirements.