A thin film transistor includes a semiconductor layer, a gate electrode, and an insulating layer. The semiconductor layer includes a source electrode, a drain electrode, and a channel part disposed therebetween. The gate electrode is disposed on the channel part and extends in a direction crossing a channel length direction of the semiconductor layer. The insulating layer includes a second region connected to the first region and extending in a same direction as an extending direction of the gate electrode from the first region. A hydrogen content of the source electrode or the drain electrode is in a range between a maximum hydrogen content that is larger than a hydrogen content of the second region of the insulating layer by about 10% and a minimum hydrogen content that is smaller than the hydrogen content of the second region of the insulating layer by about 10%.