A method for manufacturing a semiconductor device having a metallic interconnection layer is described. The method includes the steps of providing a substrate having an insulating film, forming at least one contact hole in the insulating film, forming a first metallic interconnection layer on the insulating film so that the contact hole is filled with the interconnection layer, and forming a second metallic interconnection layer on the first layer to provide a builtup structure. The second layer may be formed by a high temperature sputtering method wherein a substrate temperature is 400.degree. C. or over or by a procedure which includes forming a second metallic interconnection layer by an ordinary sputtering method and heating the substrate to a temperature not lower than 450.degree. C. to cause the second layer to be reflown. By this, the second has a smooth surface irrespective of the presence of irregularities on the surface of the first layer.