AlGaN/GaN heterostructure field effect transistors ( HFETs ) were prepared on vicinal-cut sapphire substrates. Under reverse bias, it was found that we can achieve smaller gate leakage current and smaller source-drain leakage current by using the 1 S tilted substrate. These results could be attributed to the better crystal quality and fewer crystal defects by using vicinal-cut sapphire substrates. With 2 mu m gate length, the maximum transconductance, G(m, max), was 110 mS/mm for the HFETs prepared on vicinal-cut sapphire substrates. (c) 2007 The Electrochemical Society.