A method of forming a metal wire in a semiconductor device includes performing a first etching process on an insulating layer formed on a semiconductor substrate to form a trench and an insulating layer pattern, the insulating layer pattern defining the trench. A barrier metal layer is formed over the insulating layer pattern and the trench. A second etching process is performed on the barrier metal layer to expose upper corners of the trench while leaving the trench substantially covered with the barrier metal layer. A metal layer is formed over the barrier metal layer in the trench. A heat treatment process is performed for reflowing the metal layer. The metal layer is planarized.