A study of the thermal stability of transparent conducting ZnO thin film in air is reported. By depositing a thin ZnO overlayer (similar to 10 nm) on aluminum and gallium-codoped ZnO thin film (AGZO), the thermal stability of the AGZO thin film could be significantly improved. Electrical and structural characterizations of the AGZO thin films with and without the overlayer were performed and the mechanism of the enhanced thermal stability by the overlayer was proposed. (C) 2011 Elsevier B.V. All rights reserved.