A semiconductor device includes a substrate including a first region and a second region, an active gate structure on the substrate in the first region, a dummy gate structure on the substrate in the second region, a source/drain on the substrate in the first region at each of opposite sides of the active gate structure, a plurality of first conductive contacts respectively connected to the active gate structure and the source/drain, a resistive structure on the dummy gate structure in the second region, a plurality of second conductive contacts respectively connected to the plurality of first conductive contacts and the resistive structure, and an etch stop layer between the dummy gate structure and the resistive structure. The etch stop layer includes a lower etch stop layer and an upper etch stop layer, which are formed of different materials.