Photoemissions related to the ‘‘kink’’ effect are observed in GaAs metal‐semiconductor field‐effect transistors with an Al0.2Ga0.8As/GaAs heterostructure buffer layer. In drain voltage (VDS) regions lower than the kink VDS, the photoemission mainly results from the bremsstrahlung radiation because the energy spectrum is broad between 1.1 and 1.8 eV. Near the kink VDS, photoemission results from the direct recombination process of holes generated by the impact ionization because it has a peak near at 1.4 eV. In addition, at VDS’s higher than the kink VDS, the photo intensity, as well as the drain current, saturates. It is explained by the equilibrium of the hole generation/recombination, the accumulation, and the hole current flow into the substrate.