Methods, systems, and devices are disclosed for implementing a high voltage variable resistor. In one aspect, an optical transconductance variable resistor includes a photoconductive wide bandgap semiconductor material (PWBSM) substrate, whose conduction response to changes in amplitude of incident radiation that is substantially linear throughout a non-saturation region thereof, whereby the material is operable in non-avalanche mode as a variable resistor, and first and second electrodes in contact with the material so that: a first triple junction boundary region is formed between the PWBSM substrate and the first electrode, and a second triple junction boundary region is formed between the PWBSM substrate and the second electrode, and the PWBSM substrate is located within an internal triple junction region formed between the first and second triple junction boundary regions.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the U.S. Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Laboratory.