Silicon nanocrystals on a thermally grown silicon oxide have been fabricated at a low temperature using the photo chemical vapor deposition (photo-CVD). Even at a low temperature of 150 degrees C, crystalline silicon nanocrystals are successively formed by this method. By changing the gas mixture of SiH4 and H-2, the size and number density of Si nanocrystals are systematically investigated in a controlled manner. The shape, size, and crystallinity of such nanocrystals examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). To apply Si nanocrystals in nonvolatile memory, the capacitance-voltage (CV) characteristics of Si nanocrystals are also discussed in this paper.