ZnO thin-film transistors (TFTs) with and without a thin MgZnO layer at the channel/gate insulator interface were fabricated using glass substrates. Both ZnO and MgZnO films were grown by metal organic chemical vapor deposition (MOCVD). The ZnO TFTs employing the MgZnO layer exhibit high performance with a field-effect mobility (mu(FE)) of 9.1 cm(2)/V s, a subthreshold slope (S) of 0.38 V/dec, an on/off current ratio of 2.3 X 10(8), and a turn-on voltage of -2.75 V. This is the best performance reported to date for ZnO TFTs that are realized on glass substrates with MOCVD-grown channel layers. The ZnO TFTs without the MgZnO layer, on the other hand, exhibit poor performance, and the mu(FE), S, on/off current ratio, and turn-on voltage of these devices are 2.3 cm(2)/V s, 0.78 V/dec, 6.4 X 10(7), and -6.75 V, respectively. The superior performance of ZnO TFTs with the MgZnO layer is attributed to the larger grains in the ZnO film. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3502605] All rights reserved.