The adsorption and reaction behavior of methylsilane (CH3SiH3) and disilane (Si2H6) On Si(100) single crystals has been studied using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). It was found that CH3SiH3 and Si2H6 molecules have similar adsorption behavior while ethane (C2H6) does not stick on Si(100) at 90 K. These results indicate that -SiH3 is the key functional group involved in silane adsorption. The adsorption coverage of CH3SiH3 at 90 K was found to be about twice as large as that at 300 K, indicating that methylsilane adsorbs dissociatively on Si(100) at 300 K with the breaking of the Si-C bond, producing enhanced dangling bond site blockage compared to the undissociated chemisorbed molecule. Based on the results, pentacoordinate silicon in -SiH3 groups is postulated to be involved in the nondissociative chemisorption and in the S(N)2 dissociative reaction of CH3SiH3 on dangling bond sites on Si(100).