An epoxy resin composition comprising an epoxy resin, a curing agent, (A) a carboxyl-containing benzotriazole derivative, and (B) an alkoxysilyl-containing aminoalkylsilane derivative is suited for encapsulating semiconductor devices. The sum of (A)+(B) is 0.5-5.0 pbw per 100 pbw of the sum of the epoxy resin and the curing agent, and a molar ratio (A)/(B) is 0.5-1.5. The composition is free of sulfur and highly adhesive to metal substrates.