An epoxy resin composition for encapsulating semiconductors which comprises as essential components (A) an epoxy resin, (B) a phenol resin, (C) a curing accelerator, (D) an inorganic filler and (E) a component comprising (e1) a butadiene-acrylonitrile copolymer having carboxyl group and/or (e2) a reaction product of (e1) a butadiene-acrylonitrile copolymer having carboxyl group with an epoxy resin, wherein the content of component (e1) in the entire epoxy resin composition is 0.01 to 1% by weight. The composition exhibits excellent releasing property in molding, continuous molding property and resistance to solder reflow.