Semi-insulating (SI) SiC photoconductive semiconductor switches were prepared using two compensation mechanisms: namely vanadium dopants compensation (4H- and 6H-SiC) and deep level defect compensation (4H-SiC). The bias voltage and current of the high-purity (HP) SI 4H-SiC photoconductive semiconductor switch (PCSS) with a channel length of 1 mm reached 24 kV and 364 A, respectively, and the minimum on-state resistance of approximately 1 Ω was triggered by laser illumination at a wavelength of 355 nm. The experimental results show that, in this case, the on-state characteristics of HP 4H-SiC PCSS are superior to those of the vanadium-doped(VD) 4H and 6H-SiC PCSS devices. HP 4H-SiC PCSS shows remarkable waveform consistency. Unlike for VD 4H and 6H-SiC PCSS, the current waveform of HP 4H-SiC PCSS exhibits a tailing phenomenon due to its longer carrier lifetime.