Photoconductive semiconductor switches (PCSSs) made from semi-insulating (SI) GaAs are the primary switching component of one class of high-power, ultra-wideband (UWB) microwave sources. The high resistivity of the GaAs can be achieved through different processing techniques. The resultant device characteristics of the PCSS such as breakdown voltage, rise time, and turn-on delay will depend on the actual processing technique that was used for the material. Simulation studies comparing an intrinsic material and a high resistivity SI GaAs PCSS grown through the liquid-encapsulated Czochralski (LEC) process with a deep donor and shallow acceptor compensation mechanism highlight these differences. Simulations also elucidate the role of an n+-doped layer placed next to the cathode, which increases the breakdown voltage of the device. Extending the n+ layer length beyond the cathode does not yield further improvement but leads to current confinement along a narrow strip that can initiate local heating or burnout. The doping profile of the n+ layer also affects hold-off characteristics, a faster gradient ensuring better protection of the cathode against the substrate field, and electron injection. Doping the n+ region with a higher concentration of carbon impurities does not produce the same effect as doping the n+-SI interface. These material-related issues are critical to further extending the performance characteristics of PCSSs.