A semiconductor device includes a substrate including an active region and a dummy active region that are spaced apart by an isolation layer, a buried word line extending from the active region to the dummy active region, and a contact plug coupled to an edge portion of the buried word line, wherein an upper surface of the active region is positioned at a higher level than an upper surface of the buried word line, and an upper surface of the dummy active region is positioned at a lower level than the upper surface of the buried word line.