A semiconductor device includes in an interconnect structure which includes a first interconnect made of a copper-containing metal, a first Cu silicide layer covering the upper portion of the first interconnect, a conductive first plug provided on the upper portion of the Cu silicide layer and connected to the first interconnect, a Cu silicide layer covering the upper portion of the first plug, a first porous MSQ film provided over the side wall from the first interconnect through the first plug and formed to cover the side wall of the first interconnect, the upper portion of the first interconnect, and the side wall of the first plug, and a first SiCN film disposed under the first porous MSQ film to contact with the lower portion of the side wall of the first interconnect and having the greater film density than the first porous MSQ film.