An insulating film for semiconductor devices is obtained by curing, on a substrate, a high molecular compound obtained by polymerizing a cage-type silsesquioxane compound having two or more unsaturated groups as substituents and having a cyclic siloxane structure, wherein the structure of the cage-type silsesquioxane compound is not broken by curing, and the breakage of the cage structure can be detected by observing a peak at approximately 610 cm−1 in Raman spectrum of the film after curing.