This paper presents a modified expression for the Schottky barrier height, Phi(B), that takes into account the effect of total polarization and the 2DEG concentration in GaN at the GaN/AIGaN heterointerface through the incorporation of Schottky barrier lowering. Updated Schottky barrier height for HEMTs and its dependence upon gate bias is reported. The positive surface charge is estimated to be 2.615 x 10(14) cm(-2) which corresponds to a trap level located 0.905 eV below the conduction band. 2D numerical simulations, using the modified Schottky barrier height, matches experimental data. (c) 2006 Elsevier Ltd. All rights reserved.