Schottky-type p-GaN gate gallium nitride high electron mobility transistors suffer from threshold voltage ( Vth ) instability phenomenon. Both positive and negative Vth shifts are reported when device undertakes the voltage bias, but the impact of this Vth instability phenomenon on device switching behaviors is less investigated. In this study, the drain-source voltage ( Vds ) induced bidirectional Vth shift in hard-switching condition is characterized and decoupled by an H-bridge based double-pulse test. Subsequently, the influence of Vth shift on switching behaviors is theoretically analyzed and demonstrated through SPICE simulation and experiment, showing how a positive shifted Vth can reduce the device turn- on commutation speed and increase the switching losses, and vice versa. The results suggest that the Vth instability phenomenon should be considered in accurate switching modeling.