Postfabrication rapid thermal annealing (RTA) and subsequent nitrous oxide (N2O) plasma treatment improved the performance of zinc oxide (ZnO) thin-film transistors (TFTs) in terms of off current and on/off current ratio by almost 2 orders of magnitude. The off Current of 2 x 10(-8) A and on/off current ratio of 3 x 10(3) obtained after RTA were improved to 10(-10) A and 10(5), respectively, by the subsequent N2O plasma treatment. X-ray photoelectron spectroscopy analysis of the TFT samples showed that the RTA-treated ZnO surface had more oxygen vacancies as compared to as-deposited samples, and the oxygen vacancies at the surface of RTA-treated ZnO were reduced by subsequent N2O plasma treatment. The reduction of oxygen vacancies at the top region of the ZnO channel is the cause of better off current and on/off current ratio of the TFTs. (c) 2007 The Electrochemical Society.