This method for manufacturing a SIMOX wafer includes: forming a mask layer on one surface side of a silicon single crystal wafer, which has an opening on a region where a BOX layer is to be formed; implanting oxygen ions through the opening of the mask layer into the silicon single crystal wafer to a predetermined depth, and locally forming an oxygen implantation region; annealing the silicon single crystal wafer with the mask layer, and oxidizing the oxygen implantation region so as to form the BOX layer; and removing a coated oxide film that covers the whole silicon single crystal wafer which is formed in the annealing of the silicon single crystal wafer, wherein the mask layer has a lamination comprising an oxide film and either one or both of a polysilicon film and an amorphous silicon film.