A coaxial surge protector includes a housing (17) in which is situated a transmission line (10) in the form of a two-sided printed circuit board (20). The surge protector includes input (12) and output (14) signal connectors mounted on a housing and connected to the transmission line (10), and a gas discharge tube (16) electrically coupled between the transmission line (10) and circuit ground. A thermally activated shunt assembly (18) is thermally coupled to the gas discharge tube (16) and senses when the gas discharge tube (16) is in an overheating condition. Upon such condition, the shunt assembly provides an electrically conductive shunt in parallel with the gas discharge tube (16) to divert current flowing through the gas discharge tube (16) to flow through the shunt assembly (18) to ground in order to minimize further overheating of the gas discharge tube (16).