PURPOSE: To remove metal Ga or the like adhering to a GaP wafer without etching the crystal surface of the GaP wafer by a method wherein cleaning fluid composed of hydrochloric acid and acetic acid mixed at a certain mixing ratio by volume is used.

CONSTITUTION: Cleaning fluid composed of hydrochloric acid and acetic acid was changed in the mixing ratio by volume of hydrochloric acid to acetic acid to check the change of the Ga content dissolved into cleaning fluid. The metal Ga content dissolved into cleaning fluid was small when the mixing ratio by volume of hydrochloric acid to acetic acid was 1:0.1 or below or 1:0.8 or above. Therefore, cleaning fluid composed of hydrochloric acid and acetic acid mixed at the mixing ratio 1:0.1 to 0.8 is used. It is found by a check that this mixed cleaning fluid is restrained from etching the crystal surface of a GaP wafer. By this setup, metal Ga or the like adhering to a GaP wafer can be removed without etching the crystal surface of the wafer.