A semiconductor device includes a material with which off-state current of a transistor can be sufficiently small; for example, an oxide semiconductor material is used. Further, transistors of memory cells of the semiconductor device, which include an oxide semiconductor material, are connected in series. Further, the same wiring (the j-th word line (j is a natural number greater than or equal to 2 and less than or equal to m)) is used as a wiring electrically connected to one of terminals of a capacitor of the j-th memory cell and a wiring electrically connected to a gate terminal of a transistor, in which a channel is formed in an oxide semiconductor layer, of the (j−1)-th memory cell. Therefore, the number of wirings per memory cell and the area occupied by one memory cell are reduced.