Photoemission is used for a large variety of experimental techniques for study of material properties. Further applications photoemission finds for electron beam generation. Development of photocathodes with high quantum efficiency requires sufficient microscopic understanding of photoemission processes. The LaB₆ is a well-known thermionic emitter, which can be used as a photocathode. Anomalous, thermally assisted increase of quantum efficiency was previously demonstrated for this material. The increase shows a bi-exponential rise with photon-energy dependent slopes. The photon-energy dependency indicates correlation of extracted current with electronic band structure. In this work, we have investigated possible mechanisms, which could be the reason for the anomalous dependence of photoemission current on the cathode temperature. In particular, the Fowler–DuBridge theory was modified to account for changes in the electron density of states. The results show negligible low influence of density of states structure. Finally, we make a suggestion regarding the modification of the electron escape probability, which can cause the increase in photoemission.