Abstract: In recent years, the third-generation power semiconductor devices represented by gallium nitride (GaN) materials have begun to be widely used in high-pressure, high-temperature, and high-frequency working conditions. Timely and efficient non-destructive testing of devices can reduce or avoid losses caused by device damage in these conditions. Based on the acoustic emission detection technology, this paper detects and analyzes the mechanical stress wave of the Cascode GaN high electron mobility transistor (HEMT), which is widely used at present. Multiple sets of repetitive experiments are carried out on the cooling surface and the package surface of the device, and the acoustic emission probe is used to acquire its acoustic signals while working, and analyzes the signals after filtering. At last, the characteristics and changing laws of the device's turn-on and turn-off stress wave parameters are summarized. The purpose is to explore the influence of device mechanical stress wave by drain-source voltage and gate-source voltage, and lay the foundation for the power cycling aging test to establish the connection between the device's health status and its mechanical stress wave. transistor (HEMT); mechanical stress wave; drain-source voltage; gate-source voltage