Photoemissive yield measurements were performed on degenerate n‐type and semi‐insulating GaN for heat‐cleaned and for cesiated surfaces. The photoemissive threshold for heat‐cleaned n‐type material occurs at 4.1 eV, while that for semi‐insulating material is beyond 5.5 eV, the experimental spectral range. From these measurements an upper and a lower limit of the electron affinity of heat‐cleaned GaN is derived, namely 4.1 > χ > 2.1 eV. The threshold for cesiated surfaces on both materials is lowered to 1.5 eV, and the photoyield curve exhibits a second threshold at about 3.4 eV. The occurrence of negative electron affinity is suggested for cesiated semi‐insulating GaN.
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