A semiconductor encapsulating epoxy resin composition is provided comprising (A) an epoxy resin, (B) a phenolic resin curing agent, (C) a molybdenum compound, (D-i) an organopolysiloxane, (D-ii) an organopolysiloxane cured product, or (D-iii) a block copolymer obtained by reacting an epoxy resin or alkenyl group-bearing epoxy resin with an organohydrogenpolysiloxane, and (E) an inorganic filler. The composition has improved moldability and solder crack resistance while exhibiting high flame retardance despite the absence of halogenated epoxy resins and antimony oxide.