Abstract: A trigatron switch was designed for a gigawatt nanosecond pulse source of Tesla type. For achieving subnanosecond jitter, experimental research was conducted under different voltage polarity combination, trigger voltage, trigger gap, trigger pin diameter and trigger pulse width. The results show that voltage polarity combination, trigger voltage and trigger gap have significant influence on triggering characteristics. The influence of trigger pin diameter and trigger pulse width is relative small. The trigatron switch was optimized according to the experimental results and a jitter of 0.1 ns was achieved.