PURPOSE: To suppress or prevent abnormal growth of large crystal grains and to manufacture a PTC thermistor having an improved voltage resistance characteristic by adding, together with SiO2, or instead of SiO2, nonoxide ceramic powder to calcined powder of BaTiO3 semiconductor porcelain composition, mixing the mixture, then molding in a desired shape, baking the molded form in a nonoxidative atmosphere, and oxidizing it by heat.

CONSTITUTION: Nonoxide ceramic powder having a low sintering property is mixed, together with SiO2 or instead of SiO2, with PTC thermistor material before molding, i.e., calcined powder of BaTiO3 semiconductor porcelain composition, then baked to suppress or prevent abnormal growth of crystal grains in a baked material. The baking operation is conducted in an inert nonoxidative atmosphere such as Ar, He, N2, etc., so that the powder does not sinter. The powder is further heat-treated in an oxidative atmosphere to recover its PTC characteristic. The obtained PTC thermistor has satisfactory voltage resistance characteristic without abnormally grown large crystal grain.