Low‐temperature quenching of inhomogeneities in two‐dimensional infrared images of large diameter liquid encapsulated Czochralski (LEC) crystals of semi‐insulating GaAs is reported. The temperature and wavelength dependence of the ‘‘fatiguing’’ phenomena have the same characteristics as those reported for the deep donor EL2. These results demonstrate in a clear way that the dominant nonuniformities of the infrared (0.7–1.4 eV) transmission of LEC GaAs are due to fluctuations in the concentration of neutral EL2. In the quenched state, weak nonuniformities with reverse contrast to EL2 still remain. These may be due to a photoelastic effect in the strain fields of dislocations, or to the presence of another center whose spatial fluctuations are the reverse of those of EL2.