To provide an epoxy resin composition for encapsulating a semiconductor which contains neither halogen type nor antimony type flame retardants, has flowability before the cure and after the cure excels in flame retardancy, heat resistance and moisture resistance.

The epoxy resin composition for semiconductor encapsulation contains, based on (A) 100 pts.wt. of an epoxy resin, (B) 50-150 pts.wt. of an acid anhydride, (C) 1-70 pts.wt. of a phosphazene compound such as hexaphenoxy cyclotriphosphazene and (D) 10-170 pts.wt. of magnesium hydroxide, and further contains (E) 40-90 wt% of an inorganic filler in the composition. The composition has a viscosity of 5,000-2,000,000 mPa s at room temperature.