A double exposure method forms first and second patterns on a cell region and a peripheral circuit region of a wafer, respectively. The method comprises performing a primary exposure through two-beam imaging of 0 order light and −1 order light or +1 order light using a photomask to form the first pattern, and performing a secondary exposure through three-beam imaging of the 0 order light and ±1 order light using the photomask to form the second pattern. Since the double exposure method is performed using the single photomask together with different illuminating systems, exposure time and the number of exposures are both decreased, thereby simplifying the overall process of manufacturing a semiconductor device.