High-performance AlGaN/GaN/AlGaN double heterojunction metal oxide semiconductor (MOS)-heterojunction field effect transistors (HFETs) with high-quality SiO2 layers deposited by photochemical vapor deposition (photo-CVD) technology were fabricated and reported. With a 1 mum gate, the maximum saturated I-ds, maximum g(m) and gate voltage swing of the photo-CVD fabricated MOS-HFETs were 755 mA/mm, 95 mS/mm, and 8 V, respectively. Even at a high temperature of 300 degreesC, the maximum saturated I-ds and maximum g(m) of the fabricated MOS-HFETs were still kept at 323 mA/mm and 41 mS/mm, respectively. Moreover, the simulation results clearly suggest that the temperature- induced degradation of saturation velocity is predominantly responsible for the degradation mechanisms of I-d,I-max and g(m,max). (C) 2004 The Electrochemical Society.