We have proposed and fabricated high performance AlGaN/GaN high-electron-mobility transistors (HEMTs), of which the breakdown voltage is considerably high and the leakage current is efficiently suppressed employing H2O annealing. We also investigated the effects of H2O annealing on the formation of GaOx film on the surface of AlGaN/GaN HEMT as well as reverse blocking characteristics including the breakdown voltage and the leakage current. We compared the reverse blocking characteristics of the AlGaN/GaN HEMTs fabricated by the proposed H2O annealing treatment with those of the HEMT by widely used O-2 annealing method. Also, we investigated the reverse blocking characteristics of HEMT fabricated without any annealing treatment. We used the smaller molecular size, higher permeation probability, and the lower activation energy of H2O than O-2. The breakdown voltage of AlGaN/GaN HEMT with the L-GD of 20 mu m employing H2O and O-2 annealing was 1674 and 1512 V, respectively. The drain leakage current of these devices using H2O and O-2 annealing was 13.1 and 60.1 nA/rnm under V-DS of 100 V and V-GS of -10 V, respectively. A conventional device without any annealing process exhibited the breakdown voltage of 598 V and the leakage current of 666.0 mu A/mm. In order to investigate the amounts of deep traps in the interface of AlGaN/GaN HEMT, we measured the pulsed I-V. A low drain current of the device under pulsed bias indicated that the GaOx, which was formed by H2O annealing, induced the deeper level and longer emission time of traps compared to the shallow ones. These may be related to the surface leakage current in the AlGaN/GaN HEMTs. (c) 2013 Elsevier B.V. All rights reserved.