A photodetector made in monolithic form in a lightly-doped substrate of a first conductivity type. This photodetector includes at least two photodiodes and includes a first region of the first conductivity type more heavily doped than the substrate extending at least between the two photodiodes; and a second region of the first conductivity type more heavily doped than the substrate and extending under the first region and under one of the two photodiodes, the first region or the second region, with the first region, delimiting a substrate portion at the level of said one of the two photodiodes, and the second region, with the first region, delimiting an additional substrate portion at the level of the other one of the two photodiodes.