Most chemoresistive gas sensors are supported by an insulating substrate, not integrable into silicon IC platforms, and need very high temperature to reach operating performance, this implies energy consumption and a risk factor in the presence of flammable gases. Therefore, porous silicon substrates represent a good choice, thanks to its chemical and physical properties. In this work we designed mesoporous silicon as substrate for gas sensors, and provided a theoretical investigation about the p-Si/PS/gas interface, by analysing the semiconductor band bending at the interface, the formation of a Schottky barrier and the consequent pinning of the Fermi level, due to the high density of surface states in porous silicon. The theoretical considerations have been verified through the experimental measurements with sensors based on p-Si substrate.