To measure the junction temperature of diodes under operating conditions, the temperature calibration curve is studied under large current conditions. To avoid the self heating by the large current conditions, pulsed currents are used in the paper. The temperature calibration curve of TO-247-2L fast recovery diode is investigated in this paper. The 0-1.5 A pulse current, of which the pulse width is 250 μs and the duty cycle is 5%, is chosen to study the temperature calibration curves under 50, 70, 90, 110, 130 ℃ respectively.#br#The results show that under the large current condition, the temperature calibration curve bends. The main reason for the bending phenomenon is that the series resistance changes with temperature increasing, which is affected by the mobilities of electrons and holes in semiconductor material. With the temperature rising, the mobility decreases, which results in the increasing of series resistance. Due to the series resistance increasing The voltage on p-n junction will be reduced. For this reason, a higher voltage is needed to obtain the same current, and the temperature calibration curve will bend.#br#There are two reasons which will lead to the temperature rising. The first reason is self-heating of devices by the power dissipation, and the second reason is that the temperature of device is heated by ambient temperature. Under the same temperature, self-heating behaviors of device by different currents will result in different series resistances. But in the paper, the results show that the series resistances under different currents are the same, which illustrates that self-heating is not the key reason for the change of series resistance. So, the temperature changing of the diode is caused by the ambient temperature rising, which verifies that the bending phenomenon of the temperature calibration curve of TO-247-2L fast recovery diode is caused by the ambient temperature rising.#br#Then, through experimental measurements and theoretical calculations, the accurate nonlinear temperature calibration curve is acquired, which can reduce the measurement errors of high current transient junction temperature.