An epoxy resin composition comprising (A) an epoxy resin, (B) a phenolic resin, (C) a curing accelerator, and (D) an effective flux component selected from among abietic acid, palustric acid, levopimaric acid and dihydroabietic acid is low volatile and exhibits improved wetting and adherent properties to solder balls. The epoxy resin composition is used to cover and encapsulate a semiconductor chip, especially as no-flow underfill material, forming a highly reliable semiconductor device.