A porous film-forming composition is provided comprising (A) a polymer obtained by hydrolytic condensation of a hydrolyzable silane having formula (1): R1n—Si—R24-n  (1) wherein R1 is a monovalent organic group or hydrogen, R2 is a hydrolyzable group or a hydroxyl group and n is an integer of 0 to 3, a hydrolyzate thereof or a partial condensate thereof, with the proviso that at least one silicon compound having an organic crosslinkable group as R1 is included, the polymer being capable of crosslinking reaction by the organic crosslinkable group, and (B) an organic solvent. The composition has improved storage stability, filling properties, adhesion and coating uniformity sufficient to form a sacrificial film which is dissolvable in a stripping solution.