The purpose of the present invention is to increase ON current of the oxide semiconductor thin film transistor. An example of the structure that attains the purpose is: a display device having a substrate and a thin film transistor of an oxide semiconductor formed on the substrate including: a thickness of a source region and a drain region is thicker than a thickness of a channel region of the oxide semiconductor, the channel region has projections at portions contacting the source region and the drain region, a thickness of the projection is thicker than a thickness of the center of the channel region, and a thickness of the projection is thicker than a thickness of the source region and the drain region.