The on-resistance of a GaAs coplanar waveguide-photoconductive switch was characterized as a function of laser photon energy, switch temperature, and applied dc electric field. An electric-field-dependent resonance at photon energies near the GaAs energy band-gap edge has been observed. This resonant behavior is believed to be caused by a competition between carrier recombination in the switch bulk and carrier sweep-out effects near the switch surface. This field-induced resonance was verified with 5, 10 and 20 micrometers switch gaps that were fabricated on three separate semi-insulating GaAs wafers. For fixed-wavelength laser sources, it has been shown that one can optimize the optical coupling by varying the switch temperature. The switch resistance decreased by a factor of three as a result of an increase in the switch temperature of 20 degree(s)C at photon energies near the absorption edge. A conductive-mode plasma model has been developed that adequately predicts the nonresonant switch behavior.