PURPOSE: To perfectly remove the reaction product adsorbed on the inner surface of a reaction chamber by introducing an alkaline aqueous solution and an acidic aqueous solution into the reaction chamber after high frequency washing and further introducing an org. solvent into the reaction chamber through a fluid inflow means to wash the reaction chamber.

CONSTITUTION: An object 5 to be treated is charged to the reaction chamber 1 of a semiconductor preparing apparatus composed of a container having at least a fluid inflow means 8, a discharge means 13 and a temp. raising means 3 to perform main reaction treatment. Next, an alkaline aqueous solution, an acidic aqueous solution and pure water are successively introduced into the reaction chamber 1 at room temp. or in a heated state along with nitrogen gas through the inflow means 8 and discharged through the discharge means 13. Continuously, the reaction chamber 1 is heated by the temp. raising means 3 and an org. solvent and pure water are successively introduced into the chamber 1 at room temp. or in a heated state along with nitrogen gas through the inflow means 8 and discharged through the discharge means 13, and the chamber 1 is heated by the temp. raising means 3 to be dried. As a result, the reaction product adsorbed on the inner surface of the reaction chamber can be perfectly removed.