The invention provides a number of semiconductor substrate manufacturing methods with which, in manufacturing a semiconductor substrate having a semiconductor layer in an insulated state on a supporting substrate, it is possible to obtain a thick semiconductor layer with a simple process and cheaply while reducing impurity contamination of the semiconductor layer to a minimum. One of these methods includes a defective layer forming step of carrying out ion implantation to a predetermined depth from the surface of a base substrate to partition off a monocrystalline thin film layer at the surface of the base substrate by a defective layer formed by implanted ions, a semiconductor film forming step of forming a monocrystalline semiconductor film of a predetermined thickness on the monocrystalline thin film layer, a laminating step of laminating the base substrate by the surface of the monocrystalline semiconductor film to the supporting substrate, and a detaching step of detaching the base substrate laminated to the supporting substrate at the defective layer.