The damage of an amorphous Ga2O3-In2O3-ZnO (a-GIZO) thin-film transistor (TFT) due to dry etching was removed by wet-cleaning treatment and characterized in terms of electrical performance. The damaged channel layer by dry etch had lower chemical bonding energy than that of the as-deposited layer due to physical bombardment. It seems to be oxygen deficient and to have a reduction of metal cation. The existence of a damaged layer in the a-GIZO TFT tends to significantly deteriorate threshold voltage, subthreshold swing, and off-current. With the wet-cleaning treatment, however, the damaged layer was successfully removed, thereby revealing significantly recovered electrical performances. X-ray photoelectron spectroscopy, Auger electron spectroscopy, and transmission electron spectroscopy analysis support the evidences such as channel-layer composition, chemical bonding structure, and cross structure.