Samples of n-type AlxGa1-xAs were prepared by liquid phase epitaxy on a GaAs substrate. When x≳0.4 the material has the indirect band structure characteristic of AlAs. Longitudinal piezoresistance measurements were performed on this material with stress along the 〈100〉 and 〈111〉 crystallographic directions. The results indicate that the lowest conduction-band minima in the alloy, and by inference in pure AlAs, lie along the 〈100〉 directions in k space as in silicon. © 1971 The American Institute of Physics.