The invention belongs to the technical field of high-voltage, large-power devices and in particular relates to a method for manufacturing a semiconductor substrate of a large-power device. According to the method, the ion implantation is carried out on the front face of a floating zone silicon wafer first, then a high-temperature resistant metal is used as a medium to bond the back-off floating zone silicon wafer, and a heavily CZ-doped silicon wafer forms the semiconductor substrate. After bonding, the floating zone silicon wafer is used to prepare an insulated gate bipolar transistor (IGBT), and the heavily CZ-doped silicon wafer is used as the low-resistance back contact, so the required amount of the floating zone silicon wafers used is reduced, and production cost is lowered. Meanwhile, the back metallization process is not required after bonding, so the processing procedures are simplified, and the production yield is enhanced.