Gallium Nitride based devices are not new. They have been studied since the 1980s. The first devices based on gallium nitride were LEDs, which have been widely used over the past 20 years. Then AlGaN/GaN heterostructural field-effect transistors, or high electron mobility transistors (HEMTs), featuring high power and operating frequency appeared. They are mainly used in high-frequency power amplifiers for military and civil applications. Today, with increasing demands to reduce power consumption and reduce the size of electronic equipment, the GaN transistor has turned out to be one of the most promising devices that can replace high-power silicon field-effect transistors in compact switching power supplies, DC/DC converters, smart power networks, and electric drives.