An easy and very reproducible method to produce porous silicon by light‐stimulated etching of crystalline silicon in HF is described, and the formation mechanism is discussed in terms of carrier diffusion and band bending near the surface. The method avoids the use of electrodes and electrochemical etching. The photosynthesized porous silicon shows bright photoluminescence. Spectra recorded at room temperature forn‐type as well asp‐type silicon are presented. ©1995 American Institute of Physics.