In this article, we propose an explicit and analytic charge-based model for estimating short-channel effects (SCEs) in GaN high-electron-mobility transistor (HEMT) devices. The proposed model is derived from the physical charge-based core of the ecole Polytechnique Federale de Lausanne (EPFL) HEMT model, which treats HEMT as a generalized MOSFET. The main emphasis of this article is to estimate SCEs by effectively capturing 2-D channel potential distribution to calculate the reduced barrier height, drain-induced barrier lowering (DIBL), velocity saturation, and channel length modulation (CLM). The model is validated with TCAD simulation results and agreed with measurement data in all regions of operation. This represents the main step toward the design of high-frequency and ultralow-noise HEMT devices using AlGaN/GaN heterostructures.