Undoped and doped microsensors, based on tin oxide, have been prepared by the sol–gel deposition technique. The influence of the ageing of the Ti/Au interdigitated electrical contacts on the responses of the samples has been investigated. In particular, in this paper, are reported the responses of different sensors towards some gases and vapours, discussing the reproducibility, repeatability and the baseline drift during the measurements. SEM and XPS analyses of the samples were performed before and after the working period. The sensors showed a little drift, probably due to the ageing of the electrical contacts that was observed also in the SEM images. Obtained XPS results are in good agreement with SEM images.