Abstract: A nanosecond pulsed power source based on GaAs photoconductive semiconductor switches (PCSSs) and stacked Blumlein line was developed. The pulsed power source consists of four stages of plate Blumlein line, and high-density polyethylene is adopted for energy storage. The full-circuit PSpice model of the pulsed power source with actual circuit parameters was established. Two vertical PCSSs with electrode gaps being 3 mm and 10 mm wide were used. Simulation results and experimental results are given. The rise time of the 10 mm-gap switch at 23.5 kV in experiment is larger than that in simulation. A possible reason is that the transition time of the 10 mm-gap PCSS becomes larger at lower bias electric field. The experiments indicate that the output voltages are respectively up to 39.4 kV and 53 kV with charging voltages up to 13.9 kV for the 3 mm-gap PCSS and 23.5 kV for the 10 mm-gap PCSS. The voltage efficiency with the 3mm-gap PCSS in the above condition is up to 70%. In addition, the voltage efficiency drops firstly and then rises gradually to saturation as the bias enhances.