Abstract: A light activated semiconductor device comprising a semiconductor element activated by an optical signal; at least two main electrodes, mutually insulated, for passing current from the activated semiconductor element; a casing comprising these main electrodes and hermetically sealing the semiconductor element; and a light cable passing through the casing so as to transmit the optical signal to the semiconductor element, characterized in that a hermetically formed light transmitting passage is optically connected to the light cable, said passage being hermetically held by a flexible flange fixed to a part of the casing and the conductor element is connected in press-contact with the main electrodes.