The effects of electron beam irradiation on luminescence and microstructure of n‐type porous silicon (PS) have been investigated, using cathodoluminescence (CL) in the scanning electron microscope (SEM), and electron energy loss spectroscopy in the transmission electron microscope (TEM). In the SEM, the CL rapidly decreased with irradiation. It could be fully restored by boiling the samples in de‐ionized water. In the TEM, freshly restored PS emerged as Si nano‐crystallites embedded in an unstable silicon oxide. The effect of irradiation was to suppress the oxide, and also, in the case of proximity of carbon from the foil holding the sample, to change the crystallite composition to β‐SiC. © 1995 American Institute of Physics.