dSurface reaction of CH3SiH3 on the Ge(100) and Si(100) surfaces was investigated in the low-temperature region of 400-500 degrees C using ultraclean hot-wall low-pressure chemical vapor deposition (CVD) systems, whew CH3SiH3 was supplied at a partial pressure of 18 Pa for 0-240 min. On Ge(100), the concentrations of Si and C deposited at 400 degrees C and 450 degrees C saturate to the value corresponding to the single atomic layer, but these at 500 degrees C increase continuously with exposure time. Nevertheless. at all the temperatures studied, the concentration of deposited Si is nearly the same as that of deposited C. In the case of SiH4 exposure at 450 degrees C at partial pressures of 6 and 60 Pa, it was found that the Ge atoms segregate on the top surface at the early stage of Si deposition. By comparing these results, it is considered that the adsorption of CH3SiH3 suppresses the Ge segregation. On Si(100), the C deposition by CH3SiN3 has a similar tendency to that on Ge(100), but the initial deposition efficiency is lower than that on Ge(100). Moreover, the FTIR/RAS Si-hydride peak shifts to the lower wave numbers after CH3SiH3 exposure. These results suggest that CH3SiH3 is adsorbed without breaking the Si-C bond on Ge(100) and Si(100) at 400-500 degrees C.