Abstract: A new type SO₂ sensor is constituted by using both NASICON and YSZ electrolytes with Na₂SO₄ auxiliary electrodc.lt is shown that the response of sensor to SO, is Nemstian response. As the sensor is a planar construction and both electrodes are exposed to the same test gas, there is no any need for a separate reference compartment and the effect of O₂ on EMF can be eliminated. It becomes easy that sensor is miniatur-ized and incoporated on the same substrate for sensing several compenents simultaneously. KEY WORDS SO, sensor;NASICON; YSZ solid electrolyte