We fabricated amorphous oxide semiconductor films, a-(Ga1-xZnx)O-y, at room temperature on glass, which have widely tunable band gaps (E-g) ranging from 3.47-4.12 eV. The highest electron Hall mobility similar to 7 cm(2) V-1 s(-1) was obtained for E-g = similar to 3.8 eV. Ultraviolet photoemission spectroscopy revealed that the increase in E-g with increasing the Ga content comes mostly from the deepening of the valence band maximum level while the conduction band minimum level remains almost unchanged. These characteristics are explained by their electronic structures. As these films can be fabricated at room temperature on plastic, this achievement extends the applications of flexible electronics to opto-electronic integrated circuits associated with deep ultraviolet region. (C) 2016 Elsevier B.V. All rights reserved.