A semiconductor-encapsulating epoxy resin composition comprising (A) an epoxy resin, (B) a phenolic resin curing agent, (C) an inorganic filler, and (D) carbon black is prepared by mixing a carbon black feedstock and the curing agent with an organic solvent, filtering off coarse particles of carbon black which remain over a mesh sheet with an opening of 20 μm, removing the solvent from the filtrate to yield a premix of curing agent and carbon black, and kneading the premix with the remaining components.