ZnO thin film transistors (TFTs) on Si02/Si substrate were fabricated with the channel thickness ranging from 30 nm to 90 nm. It was found that the performances of ZnO TFTs greatly depended on the thickness of ZnO channel layer. As the thickness increased, the electrical characteristic curves gradually became neither able to be cut off nor saturated. The observed changes were explained from the energy band and the resistance model of the ZnO TFT. Owing to the high resistance of thinner channel, the off-current performed very low and the on-off ratio exceeded 103. With the increase of ZnO channel layer thickness, the resistance of thin-film was greatly reduced and so was the on-off ratio. (C) 2014 Elsevier Ltd. All rights reserved.