Patent ID: 8343799

Claim:
A method for manufacturing a semiconductor device, comprising the steps of: forming a gate electrode layer over a substrate having an insulating surface; stacking a gate insulating layer, an oxide semiconductor film, and a conductive film over the gate electrode layer; forming a first mask layer over the gate insulating layer, the oxide semiconductor film, and the conductive film; etching the oxide semiconductor film and the conductive film with the use of the first mask layer to form an oxide semiconductor layer and a conductive layer in a first etching step; forming a second mask layer by etching the first mask layer; and etching the oxide semiconductor layer and the conductive layer with the use of the second mask layer to form an oxide semiconductor layer having a depression, a source electrode layer, and a drain electrode layer in a second etching step, wherein the first mask layer is formed using a light-exposure mask, wherein wet etching in which an etching solution is used is employed in each of the first etching step and the second etching step, wherein the oxide semiconductor layer having the depression includes a region with a smaller thickness than a region overlapping with the source electrode layer or the drain electrode layer, and wherein an end portion of the oxide semiconductor layer having the depression has a curved surface.