1. A semiconductor device comprising: a substrate; a mounting chip bonded to the substrate; multi-stage bumps having two or more stages of bumps stacked and bonded so that the substrate and the mounting chip are electrically connected by the multi-stage bumps; and a sheet-like interposer member of a resin material provided in the stacked stages of the multi-stage bumps and having openings each formed between two diagonally arrayed bumps of the multi-stage bumps.