Modeling of GaN HEMTs is a hot field of research. The convergence and accuracy of circuit simulations heavily rely on the compact models used. For technology optimization and circuit design, a precise physical model of the GaN HEMT is essential. This chapter highlights the surface potential (SP)-based compact GaN HEMT models. A good GaN HEMT model should be taken into account of trapping effects as well as self-heating effects. SP-based modeling of GaN HEMTs requires the computation of intrinsic charges and surface potentials for the modeling of drain current and gate leakage current. This chapter also covers the modeling of E-Mode p-GaN gate GaN HEMTs. Now, most of the models used are either simplified approximation-based models or semi-empirical models or numerical calculations-based models. Among various physics-based compact analytical models, surface potential (SP)-based models are gaining attention for future compact AlGaN/GaN HEMT modeling because of two reasons: (1) A single equation can describe all regions of operations of the AlGaN/GaN HEMTs and (2) inherent symmetry.