Optical absorption coefficients have been determined at 300°and 77°K for samples of GaAs which were doped to concentrations comparable to those present in the n, p, and p+ regions of the GaAs injection laser. n-type GaAs doped with Te to 3×1017 cm-3 and 9.6×1017 cm-3 have absorption coefficients of 20 cm-1 and 10 cm-1, respectively, at 1.475 eV and 77°K. Free carrier and deep-level absorptions contribute approximately 5 cm -1 to these values. At 77°K, p-type Zn-doped samples with N A-ND equal to 1.6×1018 cm-3 exhibit in the spectral region of laser emission an absorption that increases exponentially with photon energy and probably results from transitions of electrons in acceptor states to levels in the conduction band or conduction band tail. At 1.475 eV and 77°K, the absorption coefficient of this p-type material is 225 cm-1 to which free carrier absorption contributes only 3 cm-1. For heavier Zn-doped p+ material, e.g., 7×10 19 cm-3, the value of K at 77°K and 1.475 eV is 250 cm-1 and is entirely due to free carrier absorption. For both n and p materials, a Burstein shift of the edge to higher energies is observed for the heavily doped materials in agreement with the observations of others. © 1964 The American Institute of Physics.