The present invention provides a composition for film formation which can form a porous film that excels in dielectric properties, adhesion, film consistency and mechanical strength, and that is easily thinned; a porous film and a method for forming the same, and a high-performing and highly reliable semiconductor device which contains the porous film inside. More specifically, the composition for forming a porous film comprises a solution containing an amorphous polymer which is obtained by hydrolyzing and condensing at least one silane compound expressed by the general formula (R.sup.1).sub.nSi(OR.sup.2).sub.4-n, and a zeolite sol which is formed by using a quaternary ammonium hydroxide. The method for forming a porous film comprises a coating step for coating the composition for forming a porous film; a subsequent drying step; and a porousness forming step.