A novel gate oxide deposition technique, thermal oxidation of deposited silicon (thermal-oxide), to realise a metal insulator semiconductor (MIS) structure on GaN is reported. Reduced gate leakage current and less flat-band voltage drift are achieved compared to plasma enhanced chemical vapour deposition to SiO2 deposited on GaN. The deposition and oxidation conditions have been optimised to achieve a high quality oxide/GaN interface. © The Institution of Engineering and Technology 2009.