The present paper proposes an improved charge control model of lattice-mismatched AlGaN/GaN HEMTs, valid Over the entire operating region. The model for estimation of two-dimensional electron gas (2-DEG) sheet Carrier concentration accounts for the strongly dominant spontaneous and piezoelectric polarization Lit the AlGaN/GaN heterointerface. The dependence or 2-DEG sheet carrier concentration on the aluminum Composition and AlGaN layer thickness has been investigated in detail. Current-voltage characteristics developed from the 2-DEG model include the effect of field dependent mobility, velocity Saturation and parasitic source/drain resistances. Close proximity experimental data confirms the validity of the proposed model. (C) 2002 Elsevier Science Ltd. All rights reserved.