A method of producing a thin film transistor includes: forming a gate electrode; forming a gate insulating film that contacts the gate electrode; forming, by a liquid phase method, an oxide semiconductor layer arranged facing the gate electrode with the gate insulating film provided therebetween, the oxide semiconductor layer including a first region and a second region, the first region being represented by In(a)Ga(b)Zn(c)O(d), the second region being represented by In(e)Ga(f)Zn(g)O(h), and the second region being located farther from the gate electrode than the first region; and forming a source electrode and a drain electrode that are arranged apart from each other and are capable of being conductively connected through the oxide semiconductor layer.