Many pulsed modulator applications require high-power, low-impedance closing switches. While the surface-discharge switch (SDS) is easily integrated into most systems (e.g., using a parallel-plate or coaxial geometry) and can easily be made into a low-impedance switch (e.g., operating in the multichannel mode) most designers prefer and use other types of switches (e.g., spark gaps, thyratrons, ignitrons, etc.). This is because the SDS suffers from poor voltage holdoff recovery (caused by decomposition of the switching dielectric) and from dielectric “punch-through” (caused by dielectric erosion). Thus the selection of the switching dielectric is the critical factor which must be considered by the designer if the SDS is to have a long and trouble-free lifetime. This paper reports which dielectric properties are critical’to designing a long-life SDS. Theory is correlated with experiment by evaluating the performance of a large group of polymeric and ceramic dielectrics. These dielectrics are tested in a single-channel, self-commutating SDS operating at ~ 35 kV and ~ 300 kA (oscillatory discharge) with a pulse length of ~ 20 μs (1/4 period ~ 2 μs). The performance of a dielectric is characterized by its shot-to-shot breakdown voltage and by its mass erosion. Theoretically, the voltage holdoff degradation resistance (HDR) and the arc melting/erosion resistance (AMR) of a dielectric can be qualitatively predicted from its “formativity” and its “impulsivity,” respectively. The formativity and impulsivity are figures of merit calculated from the known thermophysical properties of the dielectric. The effects produced in dielectric performance by choice of electrode material (e.g., molybdenum, graphite, and copper-tungsten) and discharge repetition rate are also discussed.