A process for the production of an electric part, comprising performing a circuit-parts-forming step including the introduction of impurities on one surface (surface A) of a semiconductor substrate, then bonding the surface A to a holding substrate, performing a back surface treatment step essentially including a polishing of an exposed surface (surface B) of the semiconductor substrate to a thickness of 100 &mgr;m or less to obtain an electric-part-formed thinned substrate and separating the thinned substrate from the holding substrate, wherein a resin composition containing a swelling inorganic compound (WC) is used for an adhesion layer and in the separating step the thinned substrate is separated from the holding substrate after decreasing the adhesive strength of the thinned substrate and the holding substrate by swelling the swelling inorganic compound (WC).