A semiconductor device includes a substrate that includes a cell region and a peripheral circuit region, a cell insulating pattern disposed in the cell region of the substrate that defines a cell active region, and a peripheral insulating pattern disposed in the peripheral circuit region of the substrate that defines a peripheral active region. The peripheral insulating pattern includes a first peripheral insulating pattern having a first width and a second peripheral insulating pattern having a second width greater than the first width. A topmost surface of at least one of the first peripheral insulating pattern and the second peripheral insulating pattern is positioned higher than a topmost surface of the cell insulating pattern.