By replacing the commonly used Ni/Au gate metallization with Pt/Ti/Au, the critical voltage for degradation of AlGaN/GaN High Electron Mobility Transistors (HEMTs) during off-state biasing stress was significantly increased. The typical critical voltage for HEMTs with Ni/Au gate metallization was around -55 V. By sharp contrast, no critical voltage was observed for the HEMTs with Pt/Ti/Au gate metallization, even up -100 V, which was the instrumental limitation in this experiment. Both Schottky forward and reverse gate characteristics of the Ni/Au degraded once the gate voltage passed the critical voltage of -55 V. There was no degradation exhibited for the HEMTs with Pt-gated HEMTs. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3578388] All rights reserved.