The influence of Sc2O3 gate dielectric thickness and of gate length of GaN metal-oxide-semiconductor field effect transistor (MOSFETs) oil saturation current, gate Current, gate breakdown voltage and threshold voltage were examined using a drift-diffusion model. The threshold voltage was directly proportional to Sc2O3 thickness and only modestly dependent on dielectric thickness. The saturation drain current was < 10(-2) A μm(-1) for all gate lengths in the range 0.5-1.0 μm devices with oxide thickness < 800 Angstrom. Gate Current is < 10(-6) A μm(-1) at 300 K even at 100 V gate bias for 0.5 μm gate lengths and dielectric thicknesses < 800 Angstrom. The gate breakdown voltage was directly proportional to dielectric thickness. The Sc2O3 also performs as an effective surface passivation layer, mitigating the effects of Virtual gates created in the gate-drain region by surface states. (C) 2003 Elsevier Ltd. All rights reserved.