A silicon wafer after being subjected to mirror polishing but before being subjected to form an epitaxial layer thereon is subjected to an ozone gas treatment that oxidizes a surface of the silicon wafer by use of ozone gas, a hydrofluoric acid gas treatment that dissolves and removes the oxidized surface of the silicon wafer by use of hydrofluoric acid gas, and a washing treatment that removes foreign substances remaining on the surface of the silicon wafer, whereby PIDs (Polishing Induced Defects) generated by the mirror polishing are forcedly oxidized, dissolved and removed. By performing epitaxial treatment thereafter, PID-induced convex defects can be prevented from generating on the surface of the epitaxial wafer.