Polarization dependent analysis for AlGaN/GaN HEMT has been done. The capacitance-voltage characteristics of lattice mismatched AlGaN/GaN modulation doped field effect transistor are obtained using charge controlled analysis for its microwave performance. The model includes the spontaneous and piezoelectric polarization effects and device transconductance and cutoff frequency are calculated. The results show excellent agreement when compared with experimental data thereby proving the validity of the model. (c) 2006 Elsevier Ltd. All rights reserved.