A semiconductor device in which a semiconductor layer is formed over a gate electrode with a large aspect ratio, thereby obtaining a channel length of a transistor which hardly causes a short-channel effect even when the transistor is miniaturized. A lower electrode is provided under the gate electrode with an insulating layer provided therebetween so that the electrode overlaps with the semiconductor layer. A potential (electric field) of the lower electrode imparts a conductivity type to the semiconductor layer overlapping with the lower electrode, so that a source region and a drain region are formed in the semiconductor layer. The gate electrode serves as a shield, so that a region in the semiconductor layer, which faces the gate electrode with the gate insulating layer provided therebetween, is not influenced by the electric field from the lower electrode.