In addition to its exciting electrooptical properties, porous silicon exhibits characteristics of interest for sensor devices. In this work, we report on a study of porous silicon layers for gas sensor applications. We describe our test system for gas sensors and investigate electrical behaviour of porous silicon layers (p-type) in oxygen gas for various fabrication conditions. The sensing mechanism is based on a gas-induced modulation of conductivity due to adsorbed molecules in the porous film. Results show that the current increases significantly as oxygen gas is adsorbed. Electrical conduction mechanisms of the sensors in ambient pressure and room temperature are proposed. The fabrication process could be easily integrated to large scale integrated technologies. The observed behaviour suggests that the application of porous silicon in future chemical gas and biological sensors is feasible. (c) 2006 Elsevier B.V. All rights reserved.