To obtain an epoxy resin composition excellent in moisture resistance, heat resistance when soldered and moldability, esp. thin wall-infilling property and the like, small in coefficient of thermal expansion, high in reliability and useful as a sealant for semiconductor devices by using a specific epoxy resin, phenol resin and silicon nitride powder.

This composition essentially comprises (A) an epoxy resin of formula I ((n) is ≥1), (B) a phenol resin of formula II [R1 is CpH2p+1; and R2 is CqH2q+1((p) and (q) are each 0 or an integer of ≥1)], (C) a methyl methacrylate-butadiene-styrene copolymer resin and (D) a silicon nitride powder having a surface oxygen content of 0.5 to 15% in the SiO2 layer of the surface and a means particle size of 10 to 50 μm, and more specifically comprises 25 to 90 wt.% of component D.