This work presents the electric behavior of porous silicon (PS) thin films when the material's surface is exposed to carbon monoxide. PS thin films were fabricated by the electrochemical anodization method of Si-c (100) substrates with resistivity [email protected] The samples were prepared at 20min anodization time and 5mA/cm^2 anodization current. Aluminum electrodes were deposited on the surface of the material by high vacuum evaporation, such that the electric conduction was parallel to the substrate's surface. The detector was placed in vacuum during 1h and then CO was allowed into the vacuum chamber. Measurements of the I-V characteristic were carried out at atmospheric pressure, in vacuum and with CO. Changes in the resistance of the material, of about [email protected], were observed in the different samples, indicating that the material is sensitive to the presence of CO and therefore suitable as gas sensor.