A 4-MV self-triggered switch based on ultraviolet (UV) illumination technology is designed and tested under approximate 800-ns rise time pulse voltage. The switch is composed of five sections in series, and each section comprises an UV-illuminating gap (UV gap) and a main gap. The voltage charged on the UV gap is obtained by a resistance–capacitance coupling circuit, which enhances synchronization with the main gap voltage. The gap distance of the 4-MV switch is determined according to the performance of the same type of switch under a shorter pulse (about 300 ns), while the characteristics of the gap under 800-ns pulse voltage is still unclear. The experimental results show that low jitter breakdown of the switch can be realized effectively when two UV gaps are functioning. The breakdown jitter percentage achieves less than 1.55% within the range of 1.0–3.2 MV. When the working scope is narrowed down to 1.4–2.1 MV, the breakdown jitter is less than 1%.