We utilized atomic layer deposition (ALD) for the growth of the ZnO channel layers in the oxide thin-film-transistors (TFTs) with a bottom-gate structure using a SiO(2)/p-Si substrate. For fundamental study, the effect of the channel thickness and thermal treatment on the TFT performance was investigated. The growth modes for the ALD-grown ZnO layer changed from island growth to layer-by-layer growth at thicknesses of >7.5 nm with highly resistive properties. A channel thickness of 17 nm resulted in good TFT behavior with an on/off current ratio of >10(6) and a field effect mobility of 2.9 without the need for thermal annealing. However, further increases in the channel thickness resulted in a deterioration of the TFT performance, or no saturation. The ALD-grown ZnO layers showed reduced electrical resistivity and carrier density after thermal treatment in oxygen. Copyright (C) 2010 John Wiley & Sons, Ltd.