Microcontact impedance spectroscopy was used to measure the electrode polarization resistance of geometrically defined, thin, circular (La0.8Sr0.2)(0.92)MnO3 (LSM) microelectrodes deposited on yttria-stabilized zirconia (YSZ) as a function of the electrode diameter (similar to 20-200 mu m). The electrode polarization resistance is proportional to the inverse of the square of the electrode diameter. This clear result indicates a rate-determining step of the oxygen reduction that is connected with the electrode area rather than depending on the length of the three-phase boundary LSM, O-2/YSZ.