An apparatus for chemical mechanical polishing includes a wafer carrier, a first electrode, a rotatable pedestal, a second electrode, and an electric current detector. The first electrode is disposed at the wafer carrier. The rotatable pedestal is positioned opposite to the wafer carrier in order to perform a polishing operation with the wafer carrier accordingly. The second electrode is disposed at the rotatable pedestal and electrically coupled to the first electrode in order to form a circuit loop. The electric current detector is between the first electrode and the second electrode.