Design principles for of a mathematical model of the semiconductor photodetector meant for the operation in specialized computer vision systems in optical section scanning are stated. Is composed a system of equations with partial derivatives describing physical processes in separate constructively prescribed segments of the photodetector structure. The general solution is obtained as a superposition of partial solutions relating to different combinations of physical actions on the structure—external light and internal electric fields—on these segments. Families of computed and experimentally obtained output coordinate characteristics of the photodetector are given. The adequacy of the model is confirmed by the similarity of these characteristics. The model can be used on different stages of projecting and operating for photodetectors of this class.