A porous film-forming composition comprising (A) a curable silicone resin having a Mn of at least 100, (B) a micelle-forming surfactant, and (C) a compound which generates an acid upon pyrolysis remains stable during storage. The composition is coated and heat treated to form a porous film which has flatness, uniformity, a low dielectric constant and a high mechanical strength so that it is best suited as an interlayer dielectric film in the fabrication of semiconductor devices.