A triggered vacuum switch (TVS) has been applied in high pulsed power systems. It is operated by using the plasma sequentially generated at a trigger device and a main electrode. Firstly, the initial plasma is ignited at the trigger device by surface flashover mechanism. Then, the main plasma, which is induced by the initial plasma, is generated at the main electrode. In general, the research on the characteristics of trigger jitter, main jitter, and delay is essential to develop a highperformance TVS. These characteristics are crucially affected by the trigger device. Accordingly, we have fabricated a trigger device with a ring electrode and measured the trigger jitter, main jitter and delay at voltage up to 20 kV. The measured values of delay are 4.3–9.6 µs, of the trigger jitter are 0.56–2.1 µs, and of the main jitter are 3.1–5.0 µs. As a next step, we plan to continue research of characteristics with a new trigger pulse generator having a rise time of hundreds of nanoseconds.