A high power converter application built with GaN HEMT was presented. The technical aspects are developed from 6-inch wafers to converter applications, covering the optimization of 6-inch GaN epitaxial layers. The processdevice model of the 6-inch GaN E/D-mode component was established. Low-side GaN HEMT logic gates ( 2MHz) for integrated circuit were designed. Finally, The high-frequency LLC resonant converter is completed.