A photo chemical etching method to form a silicon based luminescence material on crystalline silicon has been studied. An n-type Si wafer (100) having resisitivity of 0.22-0.38 or 35-45 Ohm/cm was photo chemically etched in a mixture of HF and H2O2 (HF:H2O2 = 100:17 similar to 250), and He-Ne laser (633 nm) was irradiated onto the wafer surface through the solution. A photoluminescence spectrum from the photo chemically etched silicon under a He-Cd laser excitation (325 nm) was measured. Rutherford back scattering spectroscopy measurement was carried out to calculate the thickness of the photo chemically etched silicon. Additionally an electroluminescence device using etched silicon was fabricated, In this paper, we have proposed a schematic chemical reaction model and a chemical formula of the etching process to discuss the photochemical etching mechanism. As a result, it was found that the etching time presenting a maximum intensity of photoluminescence can be explained and calculated by the etching velocity of the photochemical etching process. Additionally, we demonstrated a yellow electroluminescence from photochemically etched silicon in order to develop the future opto-electronic device on a crystalline silicon substrate. We have exhibited here the usefulness of a photochemical etching method.