An epoxy resin composition for use as a semiconductor encapsulant comprising an epoxy resin, a polyhydroxy aromatic compound as an epoxy resin curing agent and a curing promoter, said polyhydroxy aromatic compound being derived from xylene and hydroxyl group-containing naphthalene by copolycondensation with an aldehyde, the proportions of the xylene unit and the naphthalene unit being 5 to 50 and 95 to 50 mole percent respectively, an amount of said aidehyde to be used being within the range of 0.4 to 1.0 mole per mole of a sum total of the xylene and the hydroxyl group-containing naphthalene, said compound having a weight-average molecular weight of 300 to 3,000, an equivalent ratio between the epoxy groups of said epoxy resin and the phenolic hydroxyl groups of said polyhydroxy aromatic compound being within a range of 1:0.8 to 1.2 and an amount of said curing promoter being up to 3.0% by weight based on the whole epoxy resin composition basis.