In a MOS type semiconductor device, a first contact hole having a length similar to a width of source/drain diffusion layers is opened in a first layer insulation film. In the first contact hole, a refractory metal or the like is filled and a second layer insulation film is formed to cover the same. In the second layer insulation film, a second contact hole having an area smaller than that of the first contact hole is opened and, through this second contact hole, an aluminum interconnection and the source/drain regions are electrically connected. Therefore, it becomes possible to avoid decrease of ON current of a transistor owing to resistance elements of the source/drain diffusion layers and at the same time to reduce an area occupied by the aluminum interconnection to be connected to the source/drain regions on a transistor device.