A semiconductor device having improved reliability is provided. The semiconductor device has a pixel portion. The pixel portion has a TFT and a storage capacitor. The TFT and the storage capacitor has a semiconductor layer which includes first and second regions formed continuously. The TFT has the first region of the semiconductor layer including a channel forming region, a source region and a drain region located outside the channel forming region, a gate insulating film adjacent to the first region of the semiconductor layer, and a gate electrode formed on the gate insulating film. The storage capacitor has the second region of the semiconductor layer, an insulating film formed adjacent to the second region of the semiconductor layer, and a capacitor wiring formed on the insulating film. The second region of the semiconductor layer contains an impurity element for imparting n-type or p-type conductivity. The thickness of the insulating film adjacent to the second region of the semiconductor layer is thinner than that of the film on the region in which the TFT is formed.