A semiconductor device includes a substrate, a first metal interconnection provided on a first region of the substrate, and a second metal interconnection provided on a second region of the substrate. A width of the second metal interconnection is greater than a width of the first metal interconnection. The first metal interconnection includes a metal pattern. The second metal interconnection includes a lower metal pattern having a concave surface at its top, an upper metal pattern disposed on the concave surface at the top of the lower metal pattern, and a first barrier pattern interposed between the lower metal pattern and the upper metal pattern. The metal interconnections are formed by a damascene process including deposition, reflow, metal implantation, and planarization processes.