Silicon-doped, copper-compensated, semi-insulated gallium arsenide of various doping parameters was studied with respect to infrared photoconductivity. This material is used as a photoconductive switch, the bistable optically controlled semiconductor switch (BOSS). One limitation was the relatively low conductivity of the device during the on-state. Typically, silicon-doped gallium arsenide is converted to semi-insulating gallium arsenide by the thermal diffusion of copper into the GaAs:Si. It is shown that variation of the diffusion parameters can improve the on-state conductivity by the enhancement of the concentration of a copper center known as Cu/sub B/. The conductivity of the device 150 ns after irradiation from a 20-ns FWHM laser pulse ( lambda =1.1 mu m) is recorded for various incident energies. This on-state conductivity saturates at a value that is predicted by the densities of the copper levels and the mobility. >