Abstract: An encapsulant consisting of an epoxy resin composition and suitably used to encapsulate a semiconductor device which is to be surface-mounted contains(a) an epoxy resin,(b) a rubber-modified phenolic resin comprising a phenolic resin, and a methylmethacrylate-butadiene-styrene copolymer and a thermosetting silicon rubber dispersed in said phenolic resin,(c) a curing accelerator, and(d) a silica powder.

Abstract: A rubber-modified phenolic resin composition contains a novolak-type phenolic resin in which at least one modifying agent selected from the group consisting of an ABS resin and an MBS resin is homogeneously dispersed. The composition has good impact resistance and thermal shock resistance. The composition is prepared by adding at least one modifying agent described above to a novolak-type phenolic resin which is heated and melted at its softening point or more, so that the modifying agent is homogeneous dispersed in the resin. The resin composition is suitably used as a curing agent for an epoxy resin encapsulant for sealing electronic devices.