Compared with insulated-gate bipolar transistors, integrated-gate commutated thyristor (IGCT) has lower on-state voltage, higher reliability, and lower manufacturing costs, thus, making it more suitable for high-power applications. This article focuses on the full-time junction temperature extraction of IGCTs for high-power applications. An electrothermal model for IGCT is established. Nonlinear optimization and accuracy analysis of this model are performed, which proved that the model achieves good accuracy. On the basis of the electrothermal model, junction temperature during switching on, switching off, and off state is evaluated. The junction temperature during conduction is extracted based on the temperature-sensitive electrical parameter method. Combining these two schemes, a comprehensive method to extract full-time accurate junction temperature of IGCT for high-power application is proposed. An experimental platform of IGCT-based modular multilevel converters for high-power applications is built, and power cycling experiments at different voltage and current ratings of up to 2.2 kV/1.5 kA were carried out to verify the correctness and effectiveness of the proposed method. Results show the junction temperature profile over a long period. The junction temperatures of IGCT both in inverter and rectifier modes and under different power-loading conditions are compared with the proposed comprehensive method.