A metal line of a semiconductor device comprising contact plugs, a plurality of first trenches, first metal lines, a plurality of second trenches, and second metal lines. The contact plugs are formed over a semiconductor substrate and are insulated from each other by a first insulating layer. The plurality of first trenches are formed in the first insulating layer and are connected to first contact plugs of the contact plugs. The first metal lines are formed within the first trenches and are connected to the first contact plugs. The plurality of second trenches are formed over the first metal lines and the first insulating layer and comprise a second insulating layer connected to second contact plugs of the contact plugs. The second metal lines are formed within the second trenches and are connected to the second contact plugs.