The disclosure provides an N-type thin film transistor, including a poly-silicon layer, a gate layer, a source and a drain. The poly-silicon layer includes a channel region, a source region and a drain region at two side of the channel region. The gate layer is on the channel region, a projection of the gate layer on the poly-silicon layer partially overlaps the source region and the drain region, and a thickness of the gate layer on the source region and the drain region are smaller than a thickness of the gate layer on the channel region. The source region and the drain region both include a heavily-doping region and a lightly-doping region connected to the heavily-doping region, the source and the drain are respectively on the heavily-doping region of the source region and the drain, and respectively electrically connects to the heavily-doping region of the source region and the drain.