ETO is an advanced high-power semiconductor device based on hybrid integration of traditional GTO and MOSFET.The ETO has high switching speed,snubberless turn-offca-pability and low conduction loss.When ETO is conducting current,the total current will go through the integrated MOSFET.In this situation,the MOSFET acts as a small linear resistor whose voltage drop reflects the current through it.This paper discusses a method to measure the current and transfer the current information to a PWM signal whose duty cycle is proportional to the current value.The frequency of the PWM signal is also changed according to the MOSFETs junction temperature.In this way the temperature effect on the MOSFETs on-resistance is eliminated.The sensed current information is sent out through an optical fiber.So it is very easy to be received and used for control purpose.The sensed current information is also used for the built-in over-current protection purpose.The ETOs built-in current sensor,fast turn-off speed,and high current turn-off capability enable the ETO to shut down the fault cur-rent very fast in the over-current fault situation.The experimental results show that the error of ETO built-in current sensor is less than 1%.And the over-current protection function effec-tively stops the rising of the fault current in about 2μs after the over-current triggering,and shut down the fault current in about 4μs.