The ranges of solid solution of Ga2Te3 and Ga2Te3 in GaSb at 500°C have been determined by annealing powdered samples to equilibrium and measuring lattice parameters by x-ray methods. For the GaaTea alloys, periods of annealing of up to 12 months were required to give equilibrium conditions. The limits of solid solution at 500°C were found to be 36 mole % for Ga2Te3 and 10 mole % for Ga2Te3. Measurements of room temperature optical energy gap and Hall coefficient have been made for alloys containing up to 5 mole % chalcogenide. Starting with p-type GaSb, the alloys become n-type with addition of very small amounts of chalcogenide, and values of electron concentration of up to 4 × 1017/cc and 2 × 1020/cc were found for telluride and selenide alloys, respectively. Corresponding minima in the values of Eg due to compensation were observed. The nonstoichiometry at low concentrations of chalcogenide which results in these values is discussed and the results compared with those for GaSb heavily doped with tellurium and selenium. © 1965, The Electrochemical Society, Inc. All rights reserved.