A medium- and high-voltage gas-insulated circuit breaker with arc quenching capability, comprising an electrical contact which is provided with a fixed element and with a movable element which can be mutually coupled and which form, upon separation, an arc channel into which a blast of gas is introduced which is generated by a gas chamber provided with an orifice which is controlled by a valve. The particularity of the invention is constituted by the fact that the valve is driven by the current that flows across the electrical contact.