We report on properties of delta-doping (delta -doping) of Si using SiH4 on GaAs singular and vicinal (001) surfaces in metalorganic vapor-phase epitaxy (MOVPE). The delta -doping was carried out on GaAs surfaces with different types of surface morphology to investigate the incorporation mechanism of Si and clarify the importance of atomic steps and kinks. It is found that the doping density is larger in vicinal substrates than singular substrates, and that it increased with misorientation angle. We also have found that catalytic decomposition of SiH4 at step and kink sites play a role for the incorporation of Si.