The thermal stability of undoped ZnO films on various insulators such as SiNx, SiOx, and SiOx/SiNx was investigated by thermal desorption spectroscopy. O-2 desorption was observed from all films at temperatures ranging from 300 to 350 degrees C. The crystallinity of the ZnO films was influenced by the insulators and strongly affected the desorption temperature of O-2. The sheet resistance (R-s) of the film is susceptible to O-2 desorption, and the Rs drastically fell over 7 orders of magnitude as O-2 desorbed. The R-s of ZnO/SiOx/SiNx and ZnO/SiOx were more stable than that of ZnO/SiNx; thus, these are suitable for use in thin-film transistors. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3238481] All rights reserved.