PROBLEM TO BE SOLVED: To provide a defect detection method of a heterogeneous SOI substrate with an oxide film by which defects can be easily detected without increasing defects.SOLUTION: The heterogeneous SOI substrate includes a semiconductor thin film of a material different from that of a base substrate on the base substrate. The defect detection method of the heterogeneous SOI substrate with the oxide film includes at least the steps of: performing thermal processing on the heterogeneous SOI substrate in the presence of oxygen to form the oxide film over a surface of the semiconductor thin film and a defect extending inward from the surface of the semiconductor thin film; etching the heterogeneous SOI substrate with which the oxide film is formed, at least twice by using fluorine containing solutions with different etching rates. thereby removing the oxide film on the surface of the semiconductor thin film and not removing the oxide film included within the semiconductor thin film by etching; performing
