Disclosed is a semiconductor device comprising a substrate, a first dielectric layer on the substrate, a first lower conductive line in the first dielectric layer, an etch stop layer on the first dielectric layer, a via-structure that penetrates the etch stop layer and connects to the first lower conductive line, a second dielectric layer on the etch stop layer, and an upper conductive line that penetrates the second dielectric layer and connects to the via-structure. The first dielectric layer includes a dielectric pattern at a level higher than a top surface of the first lower conductive line. The upper conductive line is in contact with a top surface of the etch stop layer. The etch stop layer has at an upper portion a rounded surface in contact with the via-structure.