Abstract: A method of improving the linearity of a photo detector of the kind comprising a semiconductor wafer, two resistive layers, each one covering one side of said wafer, a p-n junction separating said two layers, and one pair of electrodes on each resistive layers, each pair of electrodes defining two opposite sides of a right-angled square, whereby two portions of the resistive layers are defined, within said square. Said portions within said square are delimited electrically from the rest of said layers and the p-n junction, for instance by etching, whereby the linearity within this square is increased, and thus the useful area of the detector.