a semiconductor device having a dual damascene structure having a highly reliable multilayered interconnection is applied to the present invention . a protective film is formed on a first interconnection , and a modified sog film is then provided thereon . an etch stopper film is formed on the modified sog film , and a modified sog film is then formed . the modified sog film , the etch stopper film , and the modified sog film are etched away using a resist pattern , to form a via hole . the modified sog film is etched away using the resist pattern , to form a recess serving as a trench interconnection portion . the etch stopper film and the protective film which are exposed are removed , and the recess is filled with a conductive material , to form a conductive plug in the via hole and a second interconnection .