An insulating ink composition for forming an insulating film, which sufficiently achieves a low calcination temperature, solvent resistance and an insulating property, is provided. Furthermore, an ink composition for forming an insulating film which can form, by the printing method, fine insulating film patterns necessary for formation of highly integrated organic transistors is provided. The present invention provides an ink composition which forms an insulating film, and includes an organic solvent, a polyvinylphenol-based resin, an epoxy resin and a cross-linking aid. Particularly, the ink composition is a composition wherein the organic solvent includes an organic solvent which has a vapor pressure of 11.3×102 Pa or higher at 20° C. and a boiling point of lower than 115° C. under atmospheric pressure and an organic solvent which has a vapor pressure of less than 11.3×102 Pa at 20° C. and a boiling point of 115° C. or higher under atmospheric pressure; the ink composition includes a extender component having a volume average particle diameter of 1 to 150 nm and a silicone-based releasing component.