We report the fabrication of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with multi-MgxNy/GaN as an epitaxial buffer and using SiO2 dielectric by photochemical vapor deposition (Photo-CVD) simultaneously for surface passivation and as gate insulator. High quality SiO2 dielectric was successfully deposited onto AlGaN by Photo-CVD compared with the traditional plasma enhanced chemical vapor deposition (PE-CVD). Compared to conventional AlGaN/GaN HFET, the MOS-HFET with Photo-CVD SiO2 exhibits lower leakage current, higher breakdown voltage and channel current. It was also observed that our MOS-HFETs presented pure 1/f noise with smaller trapping effects and improved immunity to the RF current collapse. (c) 2012 Elsevier Ltd. All rights reserved.