A thin film transistor includes a gate electrode, a gate insulating film formed to cover the gate electrode, a semiconductor layer including a channel region formed over the gate electrode, a source electrode and a drain electrode including a region connected to the semiconductor layer, where at least a part of the region is overlapped with the gate electrode, an upper insulating film formed to cover the semiconductor layer, the source electrode and the drain electrode, where the upper insulating film is directly in contact with the channel region of the semiconductor layer and discharges moisture by a heat treatment and a second upper insulating film formed to cover the first protective film and suppress moisture out-diffusion.