A semiconductor wafer including an underlying layer including an insulating film having at least one recess therein and a metallic material layer formed over a top surface of the underlying layer and filling the recess, on a semiconductor substrate, is subjected to a polishing treatment while supplying a basic CMP slurry containing metal ions on the semiconductor wafer to at least partially remove the metallic material layer. Then, an organic acid which chelates the metal ions is added to the basic CMP slurry, and polishing is conducted, using the organic acid-added CMP slurry, until a surface of the insulating film is exposed.