By removing a fraction of fine particles having a particle size of less than 2 .mu.m from starting inorganic filler particles having a mean particle size of 10-50 .mu.m and adding thereto particles having a mean particle size of 0.1-2 .mu.m and a specific surface area of 3-10 m.sup.2 /g (BET), there is obtained a particulate inorganic filler having a mean particle size of 5-40 .mu.m. When a large amount of the inorganic filler is loaded in an epoxy resin composition, the composition maintains a low melt viscosity enough to mold and is effective for encapsulating a semiconductor device without causing die pad deformation and wire deformation. The encapsulated semiconductor device is highly reliable.