Indoor air quality is major health concern in our societies and European recommendations (directive 2008/50/EC) will be fulfilled with the help of efficient air quality monitoring systems. MOX gas sensors have proven their interest for the air quality monitoring in open air or indoor areas.[1] The main drawbacks of these sensors concern their stability over time and their lack of selectivity among mixtures of gases as well as in variable humidity environment. If attention has been focused on n-type semiconducting oxides, few studies have been devoted to the p-type gas sensors. Among p-type oxide semiconductors, CuO have demonstrated considerable potential for detection of gases such C2H5OH, NO2, H2S, H2, CO and NH3.[2] The mixture of n-type and p-type metal oxides have been used to modify the response gas sensor,[3] but there is still a lack of knowledge about the role of n-p heterojunction to overcome the effect of the hygrometry changes. In order to increase the sensitivity and the selectivity of semi-conducting gas sensors, SnO2, WO3, CuO and ZnO nanopowders have been synthesized by a metalorganic approach. Efficient sensitive layers were prepared using mixed binary or ternary blends that were further integrated on silicon substrates. The optimum blending of different metal oxides (n-type and p-type) was achieved by mixing the nanopowders in an organic solvent. The mixed metal oxides have been prepared as a screen-printing paste and deposited on silicon micro hotplates.[4] The gas sensing performances will be presented and discussed.