A semiconductor device includes a transistor on a substrate, a first metal layer that is on the transistor and includes a lower wire electrically connected to the transistor, and a second metal layer on the first metal layer. The second metal layer includes an upper wire that is electrically connected to the lower wire and includes a via structure in a via hole and a line structure in a line trench. The via structure includes a via portion that is in the via hole and is coupled to the lower wire, and a barrier portion that vertically extends from the via portion to cover an inner surface of the line trench. The barrier portion is between the line structure and an insulating layer of the second metal layer. The barrier portion is thicker at its lower level than at its upper level.