Physics based analytical model for predicting the device characteristics of GaN/AlGaN metal-insulator-semiconductor (MIS) HEMT architecture applicable to different crystalline forms (cubic and hexagonal) and polarity (Ga and N-polar) is developed. Poisson's equation is solved in the layers and the interdependence of sheet density in the 2-DEG (2 Dimensional Electron Gas), Fermi level and gate bias is derived from the airy well assessment by Schrodinger's equation. Accordingly threshold voltage models are developed. Based on these outcomes drain current and transconductance are formulated after incorporation of an appropriate Monte-Carlo simulation based mobility model. Various non-idealities such as source-drain access resistance, imaging charges at the interface/buffer, and velocity saturation are taken into consideration. The model is successful in providing accurate description of device operation for wide range of structural, material and dimensional parameters as confirmed by the close agreement with experimental data from different devices and can be used for optimizing device performances before fabrication. (C) 2014 Elsevier Ltd. All rights reserved.