In combination with a 650 V GaN cascode device, ASC safe operating area limits with current ratios of up to 4.25 times the nominal current are reached. Insights in the design as well as electrical, thermal, and infrared-thermography measurement results are presented. The concept enables further innovation due to reproducing application-relevant ASC waveforms without any circuit component adjustment in applications such as automotive traction inverters, electric powertrains, and power semiconductor qualification testing. This paper showcases its capabilities for the first reported ASC characterization of a GaN device, including measurements across the full temperature range from -40 °C to 150 °C.