forming a first conductive layer over a substrate;

forming a gate electrode over the first conductive layer; oxidizing a region of the first conductive layer which is not overlapped with the gate electrode to form an insulating layer after forming the gate electrode

etching the first conductive layer by using the gate electrode as a first mask;

laminating a gate insulating layer and a first semiconductor layer over the gate electrode;

forming a channel protective layer in a position overlapping the gate electrode;

forming a second semiconductor layer over the channel protective layer, wherein the second semiconductor layer contains one-conductivity type impurity;

forming a second mask over the second semiconductor layer;

etching the first and second semiconductor layers by using the second mask;

removing the second mask;

forming a second conductive layer serving as a source wiring or a drain wiring over the second semiconductor layer; and

etching the second semiconductor layer by using the second conductive layer as a third mask,

wherein the gate electrode is formed by a droplet discharge method.