a method and apparatus of determining the amount of impurities in an object with isothermal capacitance transient spectroscopy includes maintaining the object at a constant temperature while applying a predetermined voltage pulse to the object at predetermined test locations . the capacitance is measured over a predetermined time period , and the measured capacitance is processed to determine the amount of impurities in accordance with a differential coefficient obtained by differentiating the following equation used as the icts spectrum : ## equ1 ## wherein c is the capacitance and t is the time period .