We report direct evidence of steric effects in the dissociative adsorption of CH3Cl on Si{100} during the evolution of the coverage. The sticking probability (S) as a function of the amount of accumulated CH3Cl on the surface reveals the typical mobile precursor-mediated adsorption. For the Cl end collision, the decrease of S starts with a lower CH3Cl accumulation than for the CH3 end collision. Moreover, this steric effect depends on the surface temperature.