A semiconductor device is disclosed, which includes a first interlayer insulating film, a lower-layer interconnection in a first groove in the first film, a second interlayer insulating film over the first film, having a normal via hole opening to the lower-layer interconnection, a normal plug in the normal hole, a third interlayer insulating film over the second film, having a second groove opening to the normal plug, an upper-layer interconnection in the second groove, and a first dummy plug in a first dummy via hole in the second film, the first dummy via hole opening to one of the lower-layer and upper-layer interconnections, wherein a short side of the first dummy plug is larger than a minimum width of a minimum width interconnection and smaller than a minimum diameter of a minimum diameter via hole and a long side is larger than a shortest length of a shortest length interconnection.