Three oxygen donor gallium(III) halide complexes, [GaX3(O=P(TMP)3] (TMP = trimethoxylphenyl and X = Cl− (1), Br− (2) and I− (3)), are prepared by oxidation in mixed solvents from their phosphine adducts of [GaX3(P(TMP)3]. Three crystalline compounds are obtained from the solutions and their crystal structures are determined in the solid state. It is rare to generate a crystalline phase for metal–adduct compounds of this bulky ligand; in this paper, three new crystal structures are presented.