AbstractA solid state sensor for monitoring chlorine is presented. The applied method is the potentiometric partial pressure measurement via heterogeneous secondary equilibria using an appropriate solid state galvanic cell. The sensor is a planar double cell mounted on a supporting ceramic carrier. A high impedance converting circuit and a thick film heating structure are integrated. The various fabrication steps are reported. The sensor is working between 430 and 490 K. The sensitivity to chlorine ranges down to the sub‐ppm region. The response behaviour as well as interferences of water vapour and hydrogen sulfide are discussed.