Thin film transistor

A thin film transistor includes an oxide semiconductor layer including a channel region, and a source region and a drain region having a resistivity lower than that of the channel region; a gate insulating layer disposed on the channel region of the oxide semiconductor layer; a gate electrode disposed on the gate insulating layer; and an aluminum oxide layer covering the lateral surface of the gate insulating layer, and the source region and the drain region, wherein the gate insulating layer has a multi-layer structure including a first insulating layer and a second insulating layer, and the first insulating layer contains silicon oxide as a main component, and is disposed on and in contact with the channel region.