The impact of a gate insulator (GI) material on the device instability of InGaZnO (IGZO) thin film transistors (TFTs) was investigated. The IGZO TFTs with SiO2 GI showed consistently better stability against the applied temperature stress and positive/negative gate bias stress than their counterparts with SiNx GI. This superior stability of the SiO2-gated device was attributed to the reduced total density of states (DOS) including the interfacial and semiconductor bulk trap densities. Based on the Meyer-Neldel rule, the total DOS energy distribution for both devices was extracted and compared, which can explain the experimental observation. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3483787] All rights reserved.