Amorphous silicon nanotubes with periodically aligned dome-shaped interiors (see Figure) are fabricated by chemical vapor deposition using a gold catalyst. As-grown materials have a length of several tens of micrometers and diameters of 70-100 nm. The inner shape and size of the interiors in the products may be tuned by controlling the silane flow rate, producing structures ranging from nanowires to tubular structures. A growth model based on surface tension is proposed.