A novel solid-state NO2 sensor using ScSZ electrolyte and CuO + CuCr2O4 mixed-oxide electrode was found to respond rapidly, reproducibly and selectively to NO2 at 612 and 659° C. The response time of the sensor was ∼ 8 s and the recovery time was 10 s at both 612 and 659° C. The response of the sensor was found to be linearly dependent on the NO2 concentration between 5 and 30 ppm of NO2. The response of the sensor was reproducible to change in concentration of NO2 and also showed negligible cross-sensitivity to O-2, CO, and CH4 in the gas stream. © 2005 The Electrochemical Society. All rights reserved.