A method of sealing a semiconductor element which involves applying an epoxy resin composition including an epoxy resin and a phenolic resin obtained by reacting phenol, a biphenyl compound represented by the general formula (3) and benzaldehyde to a semiconductor element and curing the composition to seal the semiconductor element: wherein X in the formula (3) is a halogen, an OH group or an OCH3 group. The molar ratio of the total of the biphenyl compound and benzaldehyde relative to the phenol is from 0.27 to 0.40, and the molar ratio of benzaldehyde/biphenyl compound is from 5/95 to 40/60.