One example includes a method for surge-testing a gallium nitride (GaN) transistor device-under-test (DUT) that includes at least one GaN transistor device. The method includes inserting the GaN transistor DUT into a test fixture comprising an inductor such that the inductor is coupled to the GaN transistor device to form a switching power regulator. The method also includes operating the switching power regulator at a DUT operating voltage to generate an output current through the inductor based on a DUT input voltage and a duty-cycle. The method also includes controlling an excitation voltage source to provide a voltage surge-strike to the GaN transistor DUT. The method also includes measuring the output current and the DUT input voltage at least one of during and after the voltage surge-strike. The method further includes storing the measured output current and the measured DUT input voltage in a memory to specify device characteristics of the GaN transistor DUT.