A semiconductor device for measuring ultra low currents down to the level of single electrons or low voltages comprises a first and a second voltage supply terminal (1, 2), an input terminal (3) for receiving an electrical current or being supplied with a voltage to be measured, a bipolar transistor (5) having a base (B), an emitter (E) and a collector (C), wherein a first PN junction is formed between the base and the collector and a second PN junction is formed between the base and the emitter, wherein the emitter is coupled to the input terminal and the base is coupled to the second voltage supply terminal, and wherein the first PN junction is designed for reverse biased operation as an avalanche diode, and a quenching and recharging circuit (6) having a first terminal (7) coupled to the first voltage supply terminal and a second terminal (8) coupled to the collector (C) of the bipolar transistor (5), the quenching and recharging circuit permitting operation of the first PN junction reverse biased above the breakdown voltage of the first PN junction.