A semiconductor device having a structure which enables sufficient reduction in parasitic capacitance is provided. In addition, the operation speed of thin film transistors in a driver circuit is improved. In a bottom-gate thin film transistor in which an oxide insulating layer is in contact with a channel formation region in an oxide semiconductor layer, a source electrode layer and a drain electrode layer are formed in such a manner that they do not overlap with a gate electrode layer. Thus, the distance between the gate electrode layer and the source electrode layer and between the gate electrode layer and the drain electrode layer are increased; accordingly, parasitic capacitance can be reduced.