Abstract This study investigates the effect of the Gate-to-Source/Drain overlap structure of a GaN Schottky Source/Drain MOSFET. The Gate-to-Source overlap structure of the device allows the gate electric field to reduce the height of the Nickel(source)–GaN Schottky barrier near the SiO 2–GaN interface at the source side, injecting more thermionically generated carriers over the partially reduced Schottky barrier. Based on this Schottky barrier lowering mechanism, an analytical model was developed. The analytical model shows that the reduction of the Schottky barrier height by 0.25 eV increases the on-state drain current by two orders of magnitude, which is in agreement of the previously reported TCAD simulation result in . A specifically designed GaN Schottky Source/Drain MOSFET with the Gate-to-Source/Drain overlap structure was fabricated and characterized; the I D – V DS characteristic of the device shows that the on-state drain current of the device was increased by up to 160× compared to the same kind of device without the overlap structure (reported in Lei Ma (2007) ), which is in agreement with the analytical model described herein.