Abstract: High power optically activated switches of the semiconductor type utilizing broadbanded flashlamp as the source of light for rendering the semiconductor conductive and thus close the switch. In order that the conductivity of the semiconductor when in the "on" state be uniform over the load current carrying cross-section thereof, the semiconductor is treated to produce a tapered density of trapping or re-combination centers therein, with the density being a maximum at the semiconductor surface which faces the flashlamp. Several novel configurations of these switches are shown, including reflectors for concentrating the flashlamp output on the semiconductor, and a plurality of semiconductor switches all activated by a single light source, as well as liquid cooled semiconductors.