Aluminum was added to a solution-processed conductive indium tin oxide thin film to be optimized as a channel layer for a thin film transistor (TFT). The conductive crystalline thin film becomes an amorphous semiconductor as the band gap enlarges with increasing Al content. Also, systematic variation in TFT characteristics was observed clearly, displaying transformation to a semiconductor. At the final composition of (Al(2)O(3))(0.3)(In(2)O(3))(0.6)(SnO(2))(0.1), the film channel layer exhibits a high mobility of 13.3 cm(2) V(-1) s(-1), a high on-to-off ratio of 10(7) and a low subthreshold swing of 1.01 V/dec. (C) 2010 American Institute of Physics. [doi:10.1063/1.3442482]