The photovoltage spectra of the porous silicon/silicon (PS/Si) formed on the p-type silicon substrates of [111] and [100] orientation by different electrochemical anode etching conditions are measured. The photovoltage expressions with relation to the characteristic parameters are derived. The characteristic parameters: the bandgap, the carrier lifetime, and the intrinsic carrier concentration of the porous silicon layer, and the heterojunction barrier width of the PS/Si, are calculated from the measured photovoltage by using the theoretical expressions. Some calculated results are compared with the experiments. It is shown that the results are basically reasonable.