A new gas sensor device based on a porous silicon membrane has been fabricated. The sensible membrane has been bonded to a 1 cm2 Al2O3 substrate , where electrical contacts have been previously deposited by vacuum evaporation. In this work we present the results of DC measurements showing a good response of this device to humidity gradients. In this frame, the most striking properties of our device are its selectivity and a fast and full recovery after exposure to humidity levels up to 90%. Moreover, the new fabrication process used to realize the sensor merges the advantages typical of porous silicon with thin film ones, by means of a simple process.