A semiconductor device includes a substrate including a cell region, a peripheral region, and a boundary region therebetween, a cell device isolation pattern on the cell region of the substrate to define cell active patterns, a peripheral device isolation pattern on the peripheral region of the substrate to define peripheral active patterns, and an insulating isolation pattern on the boundary region of the substrate, the insulating isolation pattern being between the cell active patterns and the peripheral active patterns, wherein a bottom surface of the insulating isolation pattern includes a first edge adjacent to a side surface of a corresponding one of the cell active patterns, and a second edge adjacent to a side surface of a corresponding one of the peripheral active patterns, the first edge being at a height lower than the second edge, when measured from a bottom surface of the substrate.