The correlation between the sintering temperature and the NO2 sensing performances of the planar mixed-potential-type yttria-stabilized zirconia (YSZ)-based NOx sensor attached with NiO sensing electrode (SE) was studied by materials characterization techniques, such as impedance analysis, polarization analysis, scanning electron microscopy, and transmission electron microscopy. The sensing properties of the planar YSZ-based NOx sensors were investigated in the operating temperature range of 700-900 degrees C. The NO2 sensitivity of the present sensor was found to be modulated by changing the sintering temperature of NiO-SE. Rather large sensitivity (43 mV) to 100 ppm NO2 was obtained even at 800 degrees C for the sensor using the NiO-SE sintered at 1400 degrees C. A sensing mechanism that involves mixed potential at SE as well as catalysis in gas-phase reaction was discussed based on the results obtained. (c) 2005 The Electrochemical Society. All rights reserved.