We propose that the observed V‐shaped dependence of the direct gapE0(x) in (GaAs)1−xGe2xalloys is due to an order–disorder phase transition that occurs at the minimum of the ‘‘V.’’ In disordered Ge‐rich alloys, the stable phase is one in which either Ga or As atoms can occupy nominal cation and nominal anion sites with approximately equal probability; in ordered GaAs‐rich material, Ga (As) atoms preferentially occupy nominal cation (anion) sites. We calculate the order parameter for this transition using a three‐component spin Hamiltonian and mean‐field theory and evaluate the band structure of the alloys using a modified virtual‐crystal approximation, which depends on the order parameter.