There are provided an epoxy resin composition for encapsulation, which is particularly suitable for use in resin pre-setting type flip-chip mounting of a Cu post chip, and which is capable of suppressing defects due to the generation of voids; and a method for manufacturing a semiconductor device using a Cu post chip. The present invention provides an epoxy resin composition for semiconductor encapsulation for flip-chip mounting, which contains an epoxy resin (A), a curing agent (B), a curing accelerator (C), and 3 to 64 parts by weight, relative to 100 parts by weight of the component (A), of thermally thickening resin particles (D) having a volume-average primary particle diameter of 0.2 to 10 μm; and a method for manufacturing a semiconductor device by resin pre-setting type flip-chip mounting of a Cu post chip using the composition.