Conductivity measurements on epitaxially grown silicon‐dopedn‐Ga1−xAlxAs as a function of Al concentrationx, for 0.10⩽x⩽0.65 are presented. Simple two‐probe measurements were made possible by the development of a low‐resistance Ohmic contact, with the contact resistance independent ofx. A calculated three band (&Ggr;,X, andL) conductivity of Ga1−xAlxAs as a function ofxshows good agreement with the experimental results. The transition from a direct band‐gap semiconductor to an indirect one occurs atxc=0.45 at 300 °K. The device performance, however, begins to be affected at much lower Al concentration.