In this presentation, we report on the industry-first, true 1250V-rated lateral GaN HEMT based on Power Integrations’ PowiGaN technology platform. The 1250V GaN cascode device shows stable off-state leakage up to 2000V with a typical breakdown voltage of 2400V. Stable off-state leakage behavior demonstrated by the cascode device has a margin of over 600V compared to 1200V lateral GaN HEMTs reported in literature [1]. This allows significant transient overvoltage capability making it ideal for high-voltage, high-reliability applications. Reliability qualification data has been presented confirming the superiority of the 1250V device for such applications. In this work, we have also demonstrated high-efficiency flyback power supply operation at high input voltages using a 1250V InnoSwitch, further illustrating its readiness for real world use.