High quality SiO2 was successfully deposited on GaN by photochemical vapour deposition (photo-CVD) using a D2 lamp as the excitation source. It was found that the interface state density was only 8.4 × 1011 cm-2 eV-1 for photo-CVD SiO2 layers on GaN prepared at 300°C. AlGaN/GaN metal-oxide-semiconductor heterojunction field effect transistors were fabricated with photo-CVD oxide as the insulating layer. It was found that room temperature saturation Ids, maximum gm and gate voltage swing of the devices were 1220 mA mm-1, 240 mS mm-1 and 4.5 V, respectively. Even at an evaluated temperature of 300°C, the device still exhibits the maximum transconductance of 180 mS mm-1.