The semiconducting alloy (GaSb)1−x Ge2x is an example of a mixed crystalline alloy that undergoes a phase transition between its constituent crystal types. The order-disorder transition modifies both the long-range and short-range order in the alloy as a function of composition x. By using the Kikuchi approximation, the bond probabilities are calculated and then compared with EXAFS data. These calculations show that the EXAFS data are consistent with the existence in (GaSb)1−x Ge2x of “wrong” bonds of Ga-Ga and Sb-Sb. The theory also predicts a violation of Vegard's Law for the behavior of the mean bond length as a function of composition x.