Void forming composition, semiconductor device provided with voids formed using composition, and method for manufacturing semiconductor device using composition

[Problem] To provide a composition for gap formation capable of forming sacrifice areas made of a sacrificial material decomposable completely into vapor at a desired temperature, and also to provide a semiconductor device-manufacturing method using the composition. [Solution] Disclosed is a composition for gap formation comprising a polymer and a solvent: wherein said polymer comprising five or more of repeating units which are represented by at least one kind of the following formula (1) or (2): [each of Ar 1 , Ar 2 and Ar 2' is independently a substituted or unsabstituted aromatic group; and each of L 1 and L 2 is independently oxygen, sulfur, alkyl, sulfone, amide, ketone or a group represented by the following formula (3): {Ar 3 is an aromatic group; and L 3 is a trivalent atom selected from the group consisting of nitrogen, boron and phosphorus}].