First-principles calculations and statistical methods were combined to study electronic, magnetic, thermodynamic and structural properties of zincblende (III, Mn) V and (III, Cr) V magnetic semiconductor alloys, including both nitride and arsenide alloys. From phase diagrams it was observed that nitride alloys are much less stable than arsenide ones, although the former ones have more localized d-states at the Fermi level. It was observed that all alloys present an anisotropic behavior, with the strongest magnetic interaction in the< 110> direction. The relationship between the structural properties of these alloys and their electronic and magnetic characteristics (ie, their half-metallicity) was investigated.