This paper presents a low-jitter, low-trigger-threshold, high-dielectric-constant ceramic, plasma-triggered gas switch developed for pulsed power generators. We also discuss the principles behind the switch and the experiments and numerical calculations used. The electron emission and surface flashover in the trigger structure are used to create the initial plasma for switch breakdown. The experimental results show that the switch is triggered stably with a negative pulse of -50 kV peak and has a breakdown delay time jitter of 2-3 ns. In this jitter performance, the switch has a switch coefficient below 20%, and a peak current-carrying ability of at least ±5 kA in dry air at atmospheric pressure. The switch can also be reliably triggered with a switch coefficient of 49.7% and an over-voltage ratio of only 0.16 in dry air.