Novel porous silicon layers which photoluminesce and electroluminesce in an aqueous solution have been formed by oxidation of (100) silicon in anhydrous acetonitrile‐HF solutions. The novel porous structures consisted of large, noninterconnected pores, 1–2 μm diam, which grew normal to the surface. The pores were spaced 2–3 μm apart, and the length, which could be over 150 μm, was dependent on etch time and current density. Microporous structures (i.e., <100 nm), often associated with luminescence from porous silicon, were not detected by TEM, SEM, or infrared examination. The porous surface was hydride terminated, which was critical to the luminescence process. Since water and oxygen were not present during the formation of the porous structure and the pores were relatively large, neither silicon‐oxygen species (e.g., siloxenes) nor quantum size structures, appeared necessary for the generation visible luminescence from porous silicon.