A semiconductor device includes a first insulating layer on a substrate; a first contact hole passing through the first insulating layer and exposing an upper surface of the substrate; a first barrier metal layer disposed on a sidewall and at a bottom of the first contact hole and a first metal plug disposed on the first barrier metal layer and in the first contact hole. A recess region is between the first insulating layer and the first metal plug. A gap-fill layer fills the recess region; and a second insulating layer is on the gap-fill layer. A second contact hole passes through the second insulating layer and exposes the upper surface of the first metal plug. A second barrier metal layer is on a sidewall and at the bottom of the second contact hole; and a second metal plug is on the second barrier metal layer.