A method of manufacturing a semiconductor device includes forming active fins on a substrate; forming source/drain regions on the active fins on both sides of a gate structure, the gate structure extending in a direction intersecting with a direction in which the active fins extend; forming an etch stop layer on the source/drain regions; forming an interlayer dielectric layer on the etch stop layer; forming a first opening by partially removing the interlayer dielectric layer so as not to expose the etch stop layer; forming an impurity region within the interlayer dielectric layer by implanting a first impurity ion through the first opening; forming a second opening by removing the impurity region so as to expose the etch stop layer; implanting a second impurity ion into the exposed etch stop layer; and removing the exposed etch stop layer.