A high‐temperature potentiometric sensor was developed by coating a mixture of over one of the platinum electrodes of a cell with a yttria‐stabilized zirconia solid electrolyte. It showed good sensing characteristics over the temperature range of 450–550°C and concentration range of 0–10,000 ppm of in air. In particular, high sensitivity coupled with reasonably fast response and baseline recovery characteristics were observed at 450°C for concentrations below 3,000 ppm. The sensing mechanism and operating system were adequately described by a proposed mathematical model. The model relates the induced cell EMF to the various rate phenomena occurring in the oxide layer such as diffusion, adsorption, and surface catalytic oxidation of the adsorbed carbon monoxide by the gaseous oxygen.