Abstract: A device for monitoring thyristors of a high-voltage valve comprises thyristor voltage detectors coupled via light guides to a buffer storage unit through a selector. Also provided are an OR gate assembly, an adder, a memory unit, and a comparison unit, which are placed in series and coupled to a control unit. The OR gate assembly is connected to the buffer storage unit which is also coupled to the control unit. A second input of the comparison unit is connected to a second output of the adder, while its output is connected to an indicator signalling the quantity of disabled thyristors and to a unit protecting the high-voltage valve against breakdown. The selector is also connected to an indicator signalling the numbers of disabled thyristors.