The process of hole generation in GaN HEMTs during the semi-on state continues to be an active field of research. This study analyzes the VDS dependence of hole current in AlGaN/GaN HEMTs using an extended Okuto-Crowell model that accounts for both low-field onset and high-field saturation effects. The model accurately explains the non-conventional bias dependence of the measured hole current. This model enables the simulation of trap-assisted hole generation and may serve as a foundation for future TCAD studies of related phenomena, such as threshold voltage instability and the kink effect.