A semiconductor device includes a plurality of memory mats arranged in an X direction and a mat selecting circuit that activates a part of the memory mats based on a row address and maintains the rest of the memory mats inactivated. The memory mats are divided into a plurality of memory mat groups each including the same number of memory mats arranged in the X direction. The mat selecting circuit activates at least one of the memory mats included in each of the memory mat groups, while maintaining the rest of memory mats inactivated. With this operation, a portion of discontinuity does not occur in the memory mats arranged in the X direction, and thus the necessity of arranging two sub-word driver areas in the portion of discontinuity is eliminated.