The low-lying electronic states of AlP, GaP, InP, and GaAs have been probed using anion photoelectron spectroscopy and zero electronic kinetic energy spectroscopy. We observe transitions from the anion (2)Sigma(+) and low-lying (2)Pi states to the triplet ((3)Sigma(-) and (3)Pi states) and singlet ((1)Pi, (1)Sigma(+), and (1)Delta states) manifolds of the neutral species. The spectra of the triplet manifolds are particularly complex, with overlapping spin-orbit and vibrational progressions. Spin-orbit splittings, term energies, and vibrational frequencies are reported and compared to previous electronic structure calculations on the anions and neutrals, as well as to those parameters determined previously for the isovalent homonuclear diatomics Si-2, Ge-2, and Sn-2.