Assisted by UV/O3 annealing, InZnO thin-film transistors (TFTs) fabricated at a low temperature of 290°C showed a high field-effect mobility of 2.19 cm2/(V·s). This value was almost the same as that of InZnO TFTs annealed at 700°C without UV/O3 assistance. Si ions in the substrate were induced by UV irradiation and diffused into the InZnO thin film. They entered Zn ions sites in the InZnO matrix, and more oxygen vacancies and freely moving electrons were subsequently generated. Thus, a high mobility was obtained although the annealing temperature was lower than the pyrolysis temperature of the InZnO precursor.