Gate leakage current is a critical parameter for GaN HEMTs as it restricts the device performance. Gate current is affected by the quality of gate contact formed between the metal and GaN. A Schottky contact is expected to be formed when a metal is deposited on top of the GaN layer. Additionally, gate current can be used to study forward gate breakdown which is then subsequently used to analyse time dependent gate breakdown mechanisms. Therefore, the gate leakage current is crucial to the GaN HEMTs device designs and there has been some research modeling study to illustrate the gate leakage current. A numbers of models have been reported to analyze the leakage currents in HEMTs. They include Thermionic Field Emission (TFE), Thermionic Emission (TE), Poole Frenkel Emission (PFE), and Fowler–Nordheim Tunneling (FNT). For smaller level of leakage current, models such as Generation-Recombination (G-R), Defect Assisted Tunneling (DAT), Trap Assisted Tunneling (TAT), and two-dimensional variable range hopping (2D-VRH) are used. In lot of cases, different mechanisms are proposed to model the behavior of different devices without giving vivid explanation for their choice of a particular mechanism. In some cases, leakage at different gate bias voltages is modeled with different mechanisms, even at high bias. This chapter deals with Charge-Based EPFL HEMT Model, Charge-Based Compact Model of Gate Leakage and Surface-Potential-Based Modeling approach for the Gate Current in pGaN Gate HEMTs.