<p>The present invention provides an apparatus [18] capable of characterizing the ISFET membrane at an earlier stage of ISFET manufacturing process flow and thereby providing an improved ion concentration sensitivity of ISFET. A solution storage part [20] with an opening [21], said opening is to be in contact with ISFET membrane. Two electrodes [22, 24] are dipped into the solution storage part [20]. A capacitor is connected in series with one of the electrode. A capacitance-voltage characteristic between the electrodes in contact with the solution of known pH and another electrode at the back surface of the semiconductor is monitored. The shift of the capacitance-voltage characteristic is represented in voltage-pH graph and thereby sensitivity of ISFET is determined.</p>
