A semiconductor device may include active fins each of which extends in a first direction on a substrate, the active fins being spaced apart from each other in a second direction different from the first direction, a conductive structure extending in the second direction on the substrate, the conductive structure contacting the active fins, a first diffusion break pattern between the substrate and the conductive structure, the first diffusion break pattern dividing a first active fin of the active fins into a plurality of pieces aligned in the first direction, and a second diffusion break pattern adjacent to the conductive structure on the substrate, the second diffusion break pattern having an upper surface higher than a lower surface of the conductive structure, and dividing a second active fin of the active fins into a plurality of pieces aligned in the first direction.