To obtain the subject composition having excellent solder crack resistance, having improved normal-temperature storage characteristics while maintaining curability in molding, useful for a semiconductor apparatus, etc. by mixing an epoxy resin with a phenol resin curing agent in a specific ratio.

This composition comprises (A) an epoxy resin of formula I (R1 is H, methyl, ethyl or the like), (B) a phenyl resin curing agent, (C) a curing promoter and (D) fused silica powder as essential components. The amount of the curing promoter of formula II (R2 is a group of formula III or the like) is ≥50 wt.% based on the total amount of the component C. The blending ratio of the component A to the component B is 1.1-1.4 epoxy group to 1 phenolic hydroxyl group. The total amount of the component C comprises 50-90 wt.% of the curing promoter of formula II and 10-50 wt.% of triphenyl phosphine. The total amount of U and Th in the whole component is preferably ≤2 ppb.