Silicon nanotubes (SiNTs) have been grown on a porous alumina surface, without the assistance of catalysts, by molecular beam epitaxy (MBE). The flow rate of Si atoms and the corrugated porous alumina surface seem to play an important role in the continuous growth of Si tubular structures. The Figure shows a field-emission scanning electron microscopy image of the SiNTs grown on a regular array of hexagonal porous alumina.