Bottom-gated thin-film transistors (TFTs) on glass substrates were fabricated using ZnO channel layer grown by metal organic chemical vapor deposition with two different gate dielectrics. The gate dielectrics employed were plasma enhanced chemical vapor deposition prepared Si3N4 and SiO2/Si3N4 bilayer stack. The TFTs employing SiO2/Si3N4 bilayer gate dielectric exhibit a field-effect mobility of 17.5 cm(2)/V s and an on/off current ratio of 3 X 10(7). The TFTs using only Si3N4 gate dielectric, on the other hand, show a lower field-effect mobility of 4.9 cm(2)/V s an d a lower on/off current ratio of 2 X 10(7). The enhancement of device properties is attributed to a better c-axis crystal orientation, a larger grain size, and a lower density of point defects in ZnO films grown on the SiO2/Si3N4 bilayer stack. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3499348] All rights reserved.