X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) studies were used to investigate the reactions of coadsorbed CH3 and Cl-2 on Si/Cu(100). TPD results showed that the individual exposure of Si/Cu(100) to CH3 and Cl-2 resulted primarily in the desorption of (CH3)(3)SiH and SiCl4, respectively. Coadsorption of CH3 and Cl-2 at specific surface concentrations on Si/Cu(100) resulted in the desorption of (CH3)(4-x)SiClx (x ranges from 1 to 3) species. The relative surface concentration of CH3 and Cl (resulting from Cl-2 dissociation), however, controlled the stoichiometry of the methylchlorosilane product. XPS results suggested that more Si was removed from the Si/Cu(100) surface as gaseous product when CH3 and Cl-2 were coadsorbed on the surface than when CH3 and Cl-2 were adsorbed alone.