It is desired to integrate a photoconductive semiconductor switch (PCSS) capable of holding off and switching 100 kV into a package with small parasitic inductance such that sub-nanosecond rise time is still achievable at current amplitudes of hundreds of amperes. A GaAs based PCSS is utilized, which makes it necessary to address the filamentary nature of the current, which may lead to a shortening of device lifetime. In order to design a practical package, COMSOL based 2D electric field simulations have been utilized to aid in shaping the field between the PCSS semiconductor, the electrodes, and the high voltage encapsulant. To deal with the unavoidable high field stresses in the small package, the switch is brought to voltage within a few microseconds only, and then closed. Thus, keeping the duration of voltage stress very short, and the risk of self-Triggering due to leakage current low.