A thin film transistor includes a substrate, a semiconductor layer on the substrate, a first insulating layer covering the substrate and the semiconductor layer, a first gate electrode on the first insulating layer and overlapping the semiconductor layer, a second insulating layer covering the first gate electrode and the first insulating layer, a second gate electrode on the second insulating layer and overlapping the semiconductor layer and the first gate electrode, a third insulating layer covering the second gate electrode, a first contact hole defined in the first insulating layer, the second insulating layer and the third insulating layer, and through which a portion of the semiconductor layer is exposed, and a source electrode and a drain electrode connected to the semiconductor layer through the first contact hole.