The effects of AlGaN/GaN epilayers grown by metallorganic chemical vapor deposition on a 1 degrees-tilted c-plane sapphire substrate were studied. From chemical wet etching results, we found that the etching pits density for a 1 degrees-tilted AlGaN/GaN sample is lower than that for the on-axis AlGaN/GaN sample. This result indicated that using vicinal-cut sapphire substrates might effectively reduce threading dislocations and improve the crystal quality. It also has the higher electron concentration. Finally, compared to AlGaN/GaN diodes grown on on-axis c-plane sapphire substrates, the reverse leakage current for the AlGaN/GaN diodes grown on a 1 degrees-tilted c-plane sapphire substrate was reduced by two orders of magnitude. (c) 2008 The Electrochemical Society.