The band structure of GaP–AlP(100) superlattices with unit-cell thickness up to 32 atomic layers is reported. It is found that for the expected range of band-edge discontinuity, the superlattices exhibit a direct-gap behavior—an interesting result given the indirect nature of GaP and AlP. The wave functions associated with the top of the valence band show behavior characteristic of interface states, whereas the wave functions associated with the bottom of the conduction band are characteristic of two-dimensionally confined states.