A solid-state carbon monoxide sensor was fabricated using a 9% yttria-stabilized zirconia (YSZ) disc sandwiched between two platinum thin-film electrodes. One of the electrodes was coated with a thin layer of 7 CuO · 10 ZnO · 3 Al2O3 catalyst. The sensor showed limiting current behavior at an applied voltage between 0.5 and 1.2 V. Linear response was observed with carbon monoxide in a nitrogen–oxygen mixture at high temperature and limiting current conditions. The linear carbon monoxide concentration range increased with increase in the operating temperature and its sensitivity increased from 2.437 mA · atm−1 CO at 1,023 K to 10.771 at 1,093 K. These characteristics were adequately described by the proposed mathematical model relating the response to the rate processes occurring in the catalyst layer and in the electrochemical cell under limiting current conditions. The model showed that effective sensing and high sensitivity are best obtained using a catalyst with high catalytic activity toward the test solute and proper design and fabrication of the sensor to ensure its high diffusivity in the catalyst.