A semiconductor device includes a device isolation layer provided on a substrate, the device isolation layer defining first and second sub-active patterns, first and second gate electrodes crossing the first and second sub-active patterns, respectively, and an isolation structure provided on the device isolation layer between the first and second sub-active patterns. The first and second sub-active patterns extend in a first direction and are spaced apart from each other in the first direction. The device isolation layer includes a diffusion break region disposed between the first and second sub-active patterns. The isolation structure covers a top surface of the diffusion break region.