The equilibrium geometries and energy separations of electronic states of Al3P, AlP3 and their positive ions with pyramidal structures (C-3v) are obtained by the complete active-space MCSCF (CASSCF) followed by multi-reference singles + doubles configuration interaction (MRSDCI) calculations that included 1.2 million configurations. The (1)A(1) and (3)A(2) states were found to be the ground states for Al3P and AlP3, respectively. The atomization energies, adiabatic ionization potentials, dipole moments, and other properties for the electronic states of Al3P and AlP3 are computed and discussed. (C) 1999 Elsevier Science B.V. All rights reserved.