To provide a film-forming composition having a relatively low dielectric constant, high thermal stability, high mechanical strength and high glass transition temperature, preferably being applied by spin coating and forming a good interlayer insulation film by using a polymer dielectric material enabling to fill the gaps of a surface becoming flat and also patternized, and a method for forming the film.

This film-forming composition comprises a Diels-Alder reaction product of at least 1 kind of a compound having 2 diene functional groups with at least one of a compound having 2 dienophile functional groups, wherein at least one of the above compounds is a cross-linked or cross-linkable polyphenylene having 3 groups of the above functional groups, and a photoacid-forming agent, and the method for forming the film comprises a process of irradiating an electron beam or an electromagnetic wave having 200 nm wavelength after forming the film of the film-forming composition.