An object is to provide a method for manufacturing an SOI substrate, by which defective bonding can be prevented. An embrittled layer is formed in a region of a semiconductor substrate at a predetermined depth; an insulating layer is formed over the semiconductor substrate; the outer edge of the semiconductor substrate is selectively etched on the insulating layer side to a region at a greater depth than the embrittled layer; and the semiconductor substrate and a substrate having an insulating surface are superposed on each other and bonded to each other with the insulating layer interposed therebetween. The semiconductor substrate is heated to be separated at the embrittled layer while a semiconductor layer is left remaining over the substrate having an insulating surface.