The dependence of geometrical configurations of anode, cathode and reference electrodes on overvoltage measurement was studied using yttria-stabilized zirconia as a solid electrolyte. When a reference electrode was attached beside a counter electrode and on the opposite side of a working electrode, the overvoltage of the working electrode measured with the reference electrode was smaller than the real value. The difference from the real value was based on the overvaluation of the overvoltage of the counter electrode.