The authors report on the fabrication of thin-film transistors (TFTs) using indium-tin-zinc oxides (ITZOs) as active channel layers. Transparent amorphous ITZO semiconductors were deposited at room temperature by rf-magnetron sputtering, followed by an annealing treatment at 100 °C. The electrical properties of the ITZO channel layers deposited at room temperature using rf-magnetron sputtering were investigated by controlling the oxygen partial pressure during deposition and introducing postannealing treatments. The devices operated in an n-type enhancement mode exhibited a clear pinch-off behavior and had an on-to-off ratio of ∼108 with a low off current of 3×10-13 A. A field-effect mobility of 17 cm2/V s and a subthreshold slope of 0.5 V/decade were extracted from the device characteristics. These results suggest that ITZO semiconductors show potential as channel materials that are applicable in flexible transparent TFTs.