A method for fabricating a semiconductor device is provided. The method for fabricating a semiconductor device includes forming transistors on a semiconductor substrate, each of the transistors having a gate structure and source/drain regions, forming an oxide film on the transistors, forming a mask film pattern on the oxide film, the mask film pattern comprising a first pattern having a first width and a second pattern having a second width different from the first width, removing a part of the oxide film using the mask film pattern to form first and second trenches, filling the first and second trenches with a nitride film, removing the rest part of the oxide film to form third and fourth trenches, and forming conductive contacts by filling the third and fourth trenches. A top width of each of the third trenches is equal to the first width, and a top width of each of the fourth trenches is equal to the second width.