Structure, electronic state, and energy of semiconductor binary micro-clusters, Ga x P y and Ga x P y − , having eight atoms have been computed using density functional theory (DFT) method. Structural optimization and frequency analysis are performed at the B3LYP/6-311+G(2df) level. The charge-induced structural changes of these anions have been discussed. The strong Ga-P bond is favored over the P-P bond in Ga x P y − (x+y=8), in comparison with the corresponding neutral cluster. The calculations predict the existence of previously unknown isomers (i.e. Ga 1 P 7 − , Ga 2 P 6 − , Ga 3 P 5 − , Ga 6 P 2 − , and Ga 7 P 1 − ). Among different Ga x P y and Ga x P y − (x+y=8) clusters, Ga 4 P 4 and Ga 4 P 4 − are more stable. Two types of energy separations are reported in this study, adiabatic electron affinities (ΔE AEA ) and vertical detachment energies (ΔE VDE ), wherever applicable, and are compared with those described in other published data in the literature. Adiabatic electron affinities for Ga 4 P 4 and Ga 5 P 3 are in good agreement with those obtained in the experiments. Mulliken population analyses indicate that the bonding in GaP clusters is of a mixed type.