Gallium Nitride (GaN) transistors are gaining popularity in industrial and automotive applications due to their ability to achieve high power density and higher efficiency. However, their reliability and robustness still pose limitations to their widespread adoption. Short-Circuit (SC) robustness has been widely studied in literature by means of experimental characterizations. However, less attention has been drawn to the simulation of GaN HEMTs operating in SC conditions due to the absence of accurate models that can fully describe the main phenomena impacting the SC behavior of a GaN device: such as drain current collapse and gate-leakage current increasing. In this context, this work proposes a behavioral model for the 650-V/60-A GaN HEMT, which includes both drain and gate current.The obtained drain and gate current equations were implemented and integrated into the manufacturer model of the device in the simulation environment. The proposed behavioral model is validated experimentally by means of LTSpice simulations and experimental SC results on a half-bridge hardware prototype composed of two GaN devices at different DC-link voltages. The main outcomes demonstrate a valuable accuracy improvement in comparison with the manufacturer model.