Process for the preparation of thin monocrystalline or polycrystalline semiconductor material films, characterized in that it comprises subjecting a semiconductor material wafer having a planar face to the three following stages: a first stage of implantation by bombardment (2) of the face (4) of the said wafer (1) by means of ions creating in the volume of said wafer a layer (3) of gaseous microbubbles defining in the volume of said wafer a lower region (6) constituting the mass of the substrate and an upper region (5) constituting the thin film, a second stage of intimately contacting the planar face (4) of said wafer with a stiffener (7) constituted by at least one rigid material layer, a third stage of heat treating the assembly of said wafer (1) and said stiffener (7) at a temperature above that at which the ion bombardment (2) was carried out and sufficient to create by a crystalline rearrangement effect in said wafer (1) and a pressure effect in the said microbubbles, a separation between the thin film (5) and the mass of the substrate (6).