PURPOSE: To enable the main surface of semiconductor substrate to be heat- treated without being accompanied by its substantial roughness while protective semiconductor substrate containing As to be used several times repeatedly by a method wherein the heat treatment is performed in a status wherein the main surface of semiconductor substrate containing P is in contact with the main surface of protective semiconductor substrate containing As.

CONSTITUTION: A semiconductor substrate 1 comprising InP containing P and implanted with impurity ion comprising Si is heat treated at the temperature of 850°C in the status wherein the main surface 1a of the semiconductor substrate 1 is in contact with the main surface 2a of a protective semiconductor substrate 2 comprising GaAs containing As. Through these procedures, during the heat treatment process, the evaporation of P atoms from the main surface 1a of semiconductor substrate 1 containing P composed of the P atoms can be restrained from occurring by As atoms evaporated from the protective semiconductor substrate 2 containing As so that the main surface 1a of semiconductor substrate 1 containing P may be heat treated subject to no substantial trouble.