A semiconductor device includes a first active (e.g., PMOSFET) region and an adjacent second active (e.g., NMOSFET) region on a substrate, a device isolation layer on the substrate and defining a first active pattern on the first active region and a second active pattern on the second active region, a gate electrode crossing the first and second active patterns, a first source/drain pattern and a second source/drain pattern adjacent to a side of the gate electrode, an interlayer insulating layer on the gate electrode, a first active contact penetrating the interlayer insulating layer to connect the first source/drain pattern and a second active contact penetrating the interlayer insulating layer to connect the second source/drain pattern and a buffer layer provided in an upper region of the interlayer insulating layer and interposed between the first active contact and the second active contact, wherein the buffer layer includes a material having etch selectivity with respect to the interlayer insulating layer.