Provided are a heat-curable resin composition for semiconductor encapsulation that is capable of yielding a cured product superior in tracking resistance and dielectric property, and has a favorable continuous moldability; and a semiconductor device encapsulated by a cured product of such resin composition. The heat-curable resin composition for semiconductor encapsulation contains: (A) an epoxy resin other than a silicone-modified epoxy resin, being solid at 25° C.; (B) a silicone-modified epoxy resin; (C) a cyclic imide compound having, in one molecule, at least one dimer acid backbone, at least one linear alkylene group having not less than 6 carbon atoms, at least one alkyl group having not less than 6 carbon atoms, and at least two cyclic imide groups; (D) an organic filler; and (E) an anionic curing accelerator.