The electrical conduction of free‐standing porous silicon layers, obtained from n+ silicon with various anodization currents and illumination conditions, has been investigated in vacuum as a function of the temperature in the interval 300‐210 K. The two‐contact I‐V characteristic is determined by the metal/porous silicon rectifying interface, whereas, by using the four‐contact technique, a linear dependence of the current vs voltage was found. The resistance of free‐standing samples showed a thermally activated behavior, with activation energies ranging from 0.1 to 0.44 eV. It was found that the activation energy decreased if the light intensity during the anodization was reduced. Variations of activation energy were also observed if the anodization current was changed but, in this case, it was not possible to find any correlation over the parameter range investigated. © 1996 American Institute of Physics.