Well-aligned nanocrystalline (nc)-Si/SiOx composite nanowires have been deposited on various substrates at 120 degrees C using SiCl4/H-2 in a hot-filament chemical vapor deposition reactor. Structural and compositional analyses reveal that silicon nanocrystals are embedded in the amorphous SiOx nanowires. The nc-Si/SiOx composite nanowires are transparent in the range 500-900 nm. Photoluminescence spectra of the nc-Si/SiOx composite nanowires have a broad emission band, ranging from 420 to 525 nm. Water vapor from the chamber wall plays a crucial role in the formation of the well-aligned nanowires. A possible mechanism for the formation of the composite nanowires is suggested.