Photocurrent measurements have been carried out on a series of samples consisting of porous silicon on top of crystalline silicon, in the temperature range 10-300 K. From the experimental data set, the electrical band-gap energy of porous silicon is deduced to be (1.80 ±0.01) eV, independent of sample temperature. The results are discussed with the conclusion that for the samples studied here, the electrical bandgap in porous silicon is of molecular nature and cannot be related to quantum-confinement properties of nanocrystals of elemental silicon.