The compact model of HIroshima-University Starc Igfet Model (HiSIM)_GaN for GaN-HEMT devices is reported, which solves the Poisson equation iteratively, in a similar way as the industry-standard compact HiSIM models for other semiconductor devices. The model considers all possible charges induced within the device, including the dynamically varying trap density. It is verified that the model can reproduce the 2-D-device simulation results accurately. In particular, the operation frequency dependence of the current collapse can also be captured correctly based on the trap time constant.