An object is to provide a semiconductor substrate processing method and a semiconductor substrate that prevent formation of particles from the edge part of the substrate. Silicon ions are implanted into the edge part of an SOI substrate (10) in the direction of radiuses of the SOI substrate (10) to bring a buried oxide film (2) in the edge part of the SOI substrate (10) into a silicon-rich state. Thus an SOI substrate (100) is provided, where the buried oxide film (2) has substantially been eliminated in the edge part.