An improved version of the gas spark-gap switches intended for voltages up to 200 kV (the bipolar charging up to ±100 kV) and switching currents of up to 100 kA is designed for Marx generators of the Stand-300 installation (National Research Center Kurchatov Institute). The new design is based on the existing spark-gap configuration of P-200 switches with two toroidal electrodes and a trigger electrode as a thin disk with a hole, which is located between them (“field distortion” scheme). The design of the insulating body of the switch was modified for attaining a more uniform voltage distribution, reducing the normal component of the electric field on the insulator surface, and simplifying the gas-switch design as a whole. The measured characteristics of the new gas switch are in a good agreement with the calculated ones for the selected geometry of the spark gaps.