A resin composition usable for encapsulating a semiconductor, comprising (A) an epoxy resin having two or more epoxy groups in one molecule; (B) a curing agent; and (C) inorganic composite oxide particles constituted by silicon dioxide and at least one metal oxide selected from the group consisting of oxides of metal atoms belonging to Group III and Group IV of the Periodic Table excluding silicon; a semiconductor device comprising a wiring circuit board, a semiconductor element, and the above resin composition; and a method for manufacturing a semiconductor device comprising the steps of adhering a resin sheet comprising the resin composition of claim 1 and a stripping sheet to a semiconductor circuit side of a bump-mounting wafer, removing the stripping sheet leaving only the resin composition to the wafer, and cutting the wafer into individual chips.