When an I/O number is 8 bit, a semiconductor device includes a first memory mat that is selected when X13 is (0) and X11 and X12 are (0, 0), a second memory mat that is selected when X13 is (1) and X11 and X12 are (0, 0), and a third memory mat that is selected irrespective of a value of X13 when X11 and X12 are (0, 0). When the I/O number is 16 bit, X13 is ignored, and the first to third memory mats are selected when X11 and X12 are (0, 0). In this manner, because the third memory mat is shared between so-called upper side and lower side, control is prevented from becoming complicated and an area is prevented from increasing.