Solid electrolyte based sensors have been widely studied for the detection of CO/HC and NOx at high temperature. Nevertheless, the discussion about the sensing mechanism of non-nernstian electrochemical gas sensors, with a semiconducting sensing electrode, is still open. In this work, a study of the influence of the metallic electrode under the semiconducting metal oxide Nb 2O5 on the sensor response was performed. Planar sensors based on tape-cast YSZ layers were fabricated. Two Pt or Au finger electrodes were deposited in a parallel arrangement on a single side of YSZ. One of these electrodes was covered with Nt2O5 thick film. In order to better understand the sensing mechanism, the electrical measurements were correlated with catalytic measurements performed on both sensing and reference electrodes. copyright The Electrochemical Society.