Different methods are presented for improving chemical selectivity and sensitivity of semiconductor gas sensors consisting of nanostructured thin films. Pure and doped WO3 nanoparticles, forming nanoporous layers, are used as test material. The chemical selectivity is increased by applying different operating temperatures, using temperature modulation and pattern recognition methods, and by a fluctuation enhanced spectroscopy technique. The selectivity improvement of a fluctuation enhanced sensor is compared to that of a classical resistive sensor. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.