It is an object to provide a display device including a thin film transistor which can operate at high speed and is driven at a low voltage in a drive circuit region, and a thin film transistor having high voltage-resistance and high reliability in a pixel region. Accordingly, it is an object to provide a high reliable display device which consumes less power. A display device including a pixel region and a drive circuit region over a substrate having an insulating surface is provided. A thin film transistor is provided in each of the pixel region and the drive circuit region. A channel formation region in a semiconductor layer of the thin film transistor provided in the drive circuit region is formed to be locally thin, and the thickness of the channel formation region is smaller than that in the pixel region.