A semiconductor device includes an insulating film whose relative dielectric constant is 3.4 or less, at least one conductive layer, at least one conductive plug which is electrically connected to the conductive layer to form a conduction path, at least one reinforcing material whose Young's modulus is 30 GPa or more, at least one first reinforcing plug which is connected to the conductive layer and which is formed in contact with the reinforcing material, a reinforcing metal layer which is provided in the insulating film in an area other than that where the conductive layer is formed, and which is electrically disconnected from the conductive layer and the conductive plug, and a second reinforcing plug which is connected to the under side of the reinforcing metal layer and which is formed in contact with the reinforcing material.