Synchrotron radiation excited gas source molecular beam epitaxial growth was examined using reaction gases Si2H6 and SiH2Cl2. In Si2H6, good crystallinity was obtained only at high temperature regions, where the growth rate is limited by the supply rate to the substrate surface of gas molecules or by the desorption rate of the surface-terminating hydrogen. The growth rate significantly depends on the temperature at the region of the rate limited by the hydrogen desorption. In SiH2Cl2, the growth rate was almost independent of the temperature and the crystallinity was good at all temperatures examined (400 to 550-degrees-C). Desorption of H and Cl in the form of HCl is considered.