The device characteristics of thin-film transistors (TFTs) having amorphous In-Ga-Zn-O channel layers with various chemical compositions were studied by using combinatorial synthesis techniques. The In-Ga-Zn-O films were prepared by a radio-frequency magnetron sputtering method at room temperature in mixed-gas atmosphere of argon and oxygen. The TFT libraries enabled us to systematically survey the device characteristics of the TFTs in a wide compositional range of channel materials. It is found that the TFT characteristics are very sensitive to the chemical composition ratio of In:Ga:Zn and depend also on the oxygen partial pressure during deposition. Some devices exhibited good performance of the field-effect mobility of ∼10 cm2V-1sec -1 and on-to-off current ratio of ∼108.