A method of fabricating a TFT substrate in which a thin-film transistor is formed on a substrate, includes: forming an oxide semiconductor layer above the substrate; forming a first oxide film on the oxide semiconductor layer; performing an oxidation treatment on the oxide semiconductor layer, after the first oxide film is formed; and forming a second oxide film above the first oxide film, after the oxidation treatment is performed. In the performing of the oxidation treatment, at least one parameter of the oxidation treatment is set, based on a predetermined relationship between the at least one parameter and the threshold value of the thin-film transistor, so that the threshold value becomes a predetermined value.