A thin film transistor includes a gate electrode. The thin film transistor further includes an oxide semiconductor layer which includes at least indium and is usable as a channel layer, wherein a region of the oxide semiconductor layer closest to the gate electrode includes fluorine. The thin film transistor further includes a gate insulating layer between the gate electrode and the oxide semiconductor layer. The thin film transistor further includes a fluorine-including layer which includes fluorine and is between the gate electrode and the gate insulating layer.