Abstract: This paper presents a simplified method which can model GaN High Electron Mobility Transistor (HEMT)based on the surface-potential. Considering the mechanism of surface-potential and the diversification of high density of the carrier concentration, we first integral of the quasi-Fermi potential effect to the equation and built the new source equation of the surface-potential,and finish the explicit surface-potential-based compact core model which includes the accumulation and transitional region physics-based modeling. This modeling approach will break the existed modeling technology and provide creditable core equation and theoretical foundation. The SP-based compact core model for GaN HEMTs is verified by the Pao Sah implicit model and have good compliable with TCAD data over the applied terminal biases. This SP-based model can more accurately predict GaN HEMT current and charge behavior under varying operating conditions.