This study investigates the gate degradation mechanisms of Schottky p-GaN gate HEMTs systemically. The constant gate bias stress is applied to investigate the gate breakdown. Schottky p-GaN Gate HEMTs show a shorter gate lifetime as gate bias increases. The gate leakage current after gate breakdown shows a resistance-like characteristic. The equivalent circuit has been proposed to discuss the gate breakdown mechanisms. When applying a high gate bias for a long time, the high electric field will damage the p-GaN gate and passivation interface and generate the percolation path. The primary gate breakdown happens between the gate and source and results in a resistance-like I-V characteristic.