To obtain the subject composition that can manifest resistance against humidity without damage to flame retardancy, can secure the safety from the view point of the environmental hygiene and is useful for semiconductor sealing by using a specific red phosphorus flame retarder to increase its dispersion and enable the amount of the red phosphorus to be reduced.

This composition comprises (A) an epoxy resin, (B) a phenolic resin curing agent, (C) a red phosphorus flame retarder (preferably yellow phosphorus is directly made into red phosphorus balls or fine particles of their aggregate and the particles are coated their surfaces with aluminum hydroxide and further with a phenolic resin to prepare particles with an average particle size of 2-8μm and the maximum size is 20μm (preferably the red phosphorus content is 90-96%), (D) a cure-promoting agent and (E) an inorganic filler as essential ingredients. This composition preferably contains the component C by 0.2-2wt.%.