The effect of the adsorption of gas mixtures on current-voltage (I-V) characteristics of porous silicon (PS)-based metal-insulator-semiconductor (MIS)-structures was studied. The PS morphology was characterized by scanning electron (SEM) and atomic force (AFM) microscopes. According to the parameters of electrochemical process, PS layers were found to have a different microstructure. In particular, an inorganic polymer film under an appropriate anodic bias coats the surface of PS. Furthermore, it was found that the polymer film on PS surface influences on chemisorption of the test gas molecules. This effect may be associated with the electrical conductivity of such polymer layers, and it has been discussed using the energy band diagram of Schottky-like structures. (C) 2004 Elsevier B.V. All rights reserved.