There is described a semiconductor device which has an isolation region, the isolation region being polished by means of chemical-and-mechanical polishing, and which prevents occurrence of variations in a finished state of active regions even in a case where a large isolation area is present. An isolation region for separating active regions is formed on a semiconductor wafer. An annular dummy pattern is formed in an inactive region of greater than a predetermined size, so as to surround the isolation region. An isolation region is ensured between the active regions surrounding the inactive region and the dummy pattern.