Adsorption of group IIIA nitrides (MN, M = B, Al, Ga, and In) on a model Si(111) surface has been studied by density functional theory calculations. Eight stable structures were determined for the MN adsorbed species. Their lowest energy structures are those with the adsorbate forming a bridge between the Si adatom and the Si rest atom as well as open structures with the M−N molecule attached to a Si adatom or a Si rest atom via N. The energy ordering of these stable structures varies according to the particular metal atom. The binding energy, including the basis set superposition error, of the lowest calculated minimum MN−Si(111) structure for the different metals M ranges from 5.1 to 6.0 eV.