AlGaN/GaN high electron mobility transistor (HEMT) has many attractive material properties, which make it suitable for power electronic applications. This paper described the development of packaging for high-power AlGaN/GaN high electron mobility transistors (HEMTs) on a silicon substrate. The device is attached in a V-groove copper base, and mounted on TO-3P leadframe. The proposed packaging structure is implemented on the periphery of the surface of the device to enhance thermal management. The various thermal paths from the junction to case reduce the thermal resistance. The effects of the structure design processes and its thermal resistance were investigated. Thermal characterization indicates that the thermal resistance from the GaN chip to the TO-3P package was 13.72°C/W. The investigation of temperature is measured by IR thermography microscope. The validity of module is verified by comparing it with experimental observations. The GaN device with V-groove structure has good predictive result for the electronic characteristics.