An ideal metal/III-V semiconductor contact should be made by stable and epitaxial metallic films. In principle, such a contact may be obtained by the solid state ΐnterdiffusion of a metal film with a III-V SC substrate. We studied the solid state interdiffusions in the Ni/GaAs and Ni/AlAs systems. Our starting point was the experimental determination of the Ni-Ga-As and Ni-Al-As ternary phase diagrams. The main steps of the interaction appear to be different in the two systems. During the Ni/GaAs one, three successive steps as a function of the annealing temperature are observed : first a mixture of a Ga-rich ternary phase (C phase) + NiAs, then C phase + NiAs + NiGa and at last the two binaries NiAs + NiGa where the reaction stops. In the case of the Ni/AlAs reactions, the three steps successively correspond to a mixture of NiAl + an As-rich ternary phase then NiAl + another As-rich ternary phase + NiAs and finally NiAl + NiAs. NiAs and NiAl are the key compounds in Ni/GaAs and Ni/AlAs reactions respectively and all the reaction compounds are either textured (pseudocubic NiAs and ternaries) or epitaxial (cubic binaries NiGa and NiAl).