A novel online measurement unit for capturing the collector-emitter voltage during conduction mode has been developed. This is a well-known method for the health monitoring of power semiconductors and for estimating the junction temperature. This method is shown in the literature for up to 1000 V DC-link voltages. However, an online measurement for high-voltage (4.5 kV) IGBTs demands a new approach, as existing solutions cannot be applied. The solution proposed is experimentally verified with a 4.5-kV IGBT at various junction temperatures, collector currents and collector-emitter voltages.