The invention relates to a semiconductor detector for detecting ionizing radiation. The surface barrier required for the formation of field zones in the semiconductor body (1) is created by contact between the semiconductor body (1) and an electrolyte (3) in which it is immersed. In addition, the body is cut out, in the form of a comb in the example, in such a way as to increase its active surface as much as possible. The source (8) maintains the potential difference V.sub.o between the contact (5) on the body (1) and the cathode (7). The output signal s is extracted at (6).