A radiation detector is of the type, which by use of electric signals, which indicates the position of an irradiated point on a detector surface of the detector. The detector includes a semiconductor wafer having at least two barrier layers, which are arranged in such manner that when applying an electric bias across the layers, one layer is reversely biased and the other if forwardly biased, the extension of the reversely biased barrier layer substantially coinciding with the detector surface. The detector further includes at least two conductive layers provided with at least one current collecting electrode, the conductive layers being arranged so as to allow a transistor amplification between the forwardly and reversely biased layer by use of charge currents generated by the radiation in the irradiated point and separated by the reversely biased barrier layer.