A composition for forming a gap-filling material for lithography which, as a gap-filling material for lithography superior in planarization ability on a substrate having irregularities such as holes or trenches, causing no intermixing with a resist layer, and having a high dry etching rate as compared with the resist, is used in producing semiconductor devices by a method using the gap-filling material to cover the resist on the substrate having holes having an aspect ratio, defined as height/diameter, of 1 or more to transfer images onto the substrate by utilization of lithographic process, the composition being used to coat the substrate prior to the coating of the resist so as to planarize the substrate surface, and the composition being characterized by containing a polymer solution consisting of a polymer and a solvent.