Miniature, potentiometric, solid-state CO sensors utilizing titania-based semiconducting oxide electrodes are studied at the operating temperature of the optimal response, i.e., 500 degrees C. To improve the selectivity, sensitivity, and response time, yttria and palladium were mixed into the titania electrodes. Excellent sensing performance was obtained using an assembly of titania on one side and composite titania cermet synthesized by adding yttria and palladium on the other. The use of platinum contacts instead of gold current collectors afforded a substantial improvement in voltage response. The device detected an extended range of CO concentration (1-1000 ppm) with a high sensitivity to CO, while being capable of detecting even 1 ppm variations at low CO concentration ranges and retaining considerable selectivity to CO against CO(2), NO, and O(2) gases. Additionally, the response to CO is barely influenced by the coexisting interference gases (100 ppm NO, 16% CO(2), 3% O(2), 3% H(2)O).