This article proposes a novel ultra-fast self-powered bidirectional solid-state circuit breaker (SSCB) with voltage overshoot suppression that uses gallium nitride switches with very low conduction losses. This SSCB can be used in low and medium ac/dc networks for both short-circuit protection and overcurrent protection. An exhaustive methodology for RCD snubber design applied to SSCBs is provided. A comprehensive review of the technical literature is presented exhibiting that the proposed SSCB reduces conduction losses and detection time in comparison with other similar SSCBs. The performance features of the proposed SSCB are verified through the functional tests that are carried out employing a hardware-implemented prototype. Experimental results confirm that our proposal is able to detect and process the short-circuit failure in 282 ns; the authors have not found any faster results in the literature.