Provided is an oxide semiconductor thin film transistor with low parasitic capacitance and high reliability.A thin film transistor includes a substrate, an oxide semiconductor layer including a channel region, a source region, and a drain region, a gate insulating film, and a gate electrode. The gate insulating film includes one layer or two layers, at least one of the layers of the gate insulating film is a patterned gate insulating film located at a position separated from the source electrode and the drain electrode. A length of a lower surface of the patterned gate insulating film in a channel length direction is greater than a length of a lower surface of the gate electrode in the channel length direction. The length of the lower surface of the patterned gate insulating film in the channel length direction is greater than a length of the channel region in the channel length direction. The source region and the drain region have a higher hydrogen concentration than the channel region.