The cathodoluminescence (CL) from porous silicon and thermal‐oxidized porous silicon was examined by x‐ray spectroscopy and photoluminescence (PL). Two dominant CL bands were observed at 460 nm (2.7 eV) and 650 nm (1.9 eV), respectively, which were not found in the PL spectrum. Electron beam irradiation caused degradation and/or increase in luminescence, and the two bands showed different variations. It has been concluded that electron beam excitation mainly occurs in amorphous SiO2, and the two bands are caused from different defects in amorphous SiO2covering the porous silicon. ©1995 American Institute of Physics.