To surely and efficiently fill up contact holes to obtain contact plugs having good electric characteristics, by laminating a first metal film on the inner walls of the contact holes through a barrier metal, laminating a second metal film, heat treating it to form an alloy film.

A layer insulation film 2 laminated on conductive regions 1a in a semiconductor substrate 1 or wiring thereon is selectively etched to form contact holes. A first metal layer 7 is laminated on the inner walls of the holes 3 including their bottoms through a barrier metal 4, and a second metal film 8 is laminated on its upper surface. It is heat treated to form an alloy film with the second metal films 7, 8, and the alloy film is buried in the contact holes to form contact plugs, wherein the first film 7 is laminated so as to make uniform the thickness on the inner walls of the holes 3 and is made of e.g. Cu while the second metal film 8 is made of Al.