To provide a method of manufacturing a porous silica thin film having a low specific dielectric constant and mechanical strength enough to be durable against chemical mechanical polishing (CMP) process in a copper wiring process of a semiconductor device.

A silica precursor is produced by hydrolyzing an alkoxy silane having a specific structure with a pH controlled to 4.5-8 and carrying out condensation polymerization reaction. A coating composition for the insulating thin film which contains the silica precursor, an organic polymer and a solvent is applied on a substrate under a specific condition and the silica precursor is gelated to form a thin film of a silica/organic polymer composite. After that, the insulating thin film is obtained by removing the organic polymer from the thin film.