Semiconductor sensors based on nanocrystalline SnO2, In2O3 and In2O3-SnO2 thin films have been investigated for detecting low concentration (2-20 ppm) of nitrogen dioxide in dry air. In this work the gas-sensitive layers were prepared by modified sol-gel methods making use of non-standard precursors and a suitable surfactant. The samples have been structurally and morphologically characterized by Xray diffraction and SEM, respectively. Good gas-sensing responses towards NO2 have been found for all the prepared samples with improved performances for the In2O3-SnO2 based sensor. The performances of the sensors have been discussed according to the surface chemical reactions between the gas phase and the semiconductor. (c) 2005 Elsevier B.V. All rights reserved.