Abstract In this work, high temperature planar sensors based on tape-cast YSZ layers with Nb2O5 n-type semiconducting oxide as sensing electrode were studied. The investigated gases were CO and different saturated and unsaturated hydrocarbons. A study on the presence of the metallic electrode under the metal oxide and on the nature of that metallic (Pt or Au) electrode was performed. Thus, different types of sensors were prepared and investigated. The sensors were tested in potentiometric devices at various concentrations of gases in the 500–700 °C temperature range. The most promising sensor in terms of selectivity, sensitivity and stability was Pt/YSZ/Nb2O5, without any metallic electrode under the Nb2O5 powder. In fact, this sensor was found totally selective to propylene with very large EMF response even at temperature as high as 700 °C (−115 mV/decade).