Hydrogenated nanocrystalline silicon (nc-Si:H) thin films were prepared by plasma enhanced chemical vapor deposition (PECVD) techniques. We could obtain red, green, or blue PL by controlling a kinetic variable, the flow rate of reaction gas. As the flow rate of SiH4 decreased, SiH3 became a dominant type of hydrogen-bonding on crystallite surfaces. SiH3 radicals seem to have a critical influence on crystallite size by suppressing Si crystal growth in the films. It was found that the crystallite size varied in the range of 2 similar to 8 nm with the SiH4 flow rate in this experiment.