A thin film transistor includes: a first semiconductor layer; a second semiconductor layer disposed on the first semiconductor layer; and a pair of source region and drain region formed by doping both sides of the first semiconductor layer and the second semiconductor layer with impurities, and the source region includes a first source layer on the same plane as the first semiconductor layer and a second source layer on the same plane as the second semiconductor layer, and the drain region includes a first drain layer on the same plane as the first semiconductor layer and a second drain layer on the same plane as the second semiconductor layer, and only one of the first semiconductor layer and the second semiconductor layer is a transistor channel layer.