We present an optoelectronic switch with exceptional optical sensitivity (250 fJ) operating at high speed (16 MHz). The switch consists of a differential pair of optical PnpN devices. Its excellent optical sensitivity directly ensues from the differential switching principle. The operation speed results from the use of a specially conceived PnpN layer structure, called the depleted optical thyristor, in combination with a particular operation cycle. The performance of our switch corresponds to an improvement of about five orders of magnitude in speed for comparable sensitivity, and of two orders of magnitude in optical sensitivity for the given speed as compared to that of conventional PnpN switches.