A method for producing SOS substrates which can be incorporated into a semiconductor production line, and is capable of producing SOS substrates which have few defects and no variation in defects, and in a highly reproducible manner, or in other words, a method for producing SOS substrates by: forming an ion-injection region (3) by injecting ions from the surface of a silicon substrate (1); adhering the ion-injection surface of the silicon substrate (1) and the surface of a sapphire substrate (4) to one another directly or with an insulating film (2) interposed therebetween; and then obtaining an SOS substrate (8) having a silicon layer (6) on the sapphire substrate (4), by detaching the silicon substrate in the ion-injection region (3). This method is characterized in that the orientation of the sapphire substrate (4) is a C-plane having an off-angle of 1 degree or less.