Provided are a white heat-curable epoxy resin composition capable of yielding a cured product that is tough and superior in initial reflection rate and heat resistance; and a semiconductor device with a light receiving element and other semiconductor elements being encapsulated by such cured product. The white heat-curable epoxy resin composition contains: (A) a prepolymer as a molten mixture of (A-1) an epoxy resin: a triazine derivative epoxy resin and/or an alicyclic epoxy compound having an epoxy group and an alicyclic structure in one molecule and being non-fluid at 25° C., (A-2) an acid anhydride having no carbon-carbon double bond and (A-3) an acrylic resin-based modifier having an epoxy group and a weight-average molecular weight of 1,000 to 30,000; (B) a white pigment containing a titanium oxide; (C) an inorganic filler; (D) a curing accelerator; and (E) an antioxidant.