This work investigates and compares the junction temperature of a p-type Ge infrared (IR) emitter as well as to verify the methods used for this 850nm emitter which include the thermal transient measurement, voltage-temperature characteristics and current-voltage characteristics (electrical test method). The voltage-temperature measurement involved the measurement of device voltage with the manipulation of test temperature at a fixed minimal sensing current. The current-voltage measurement involved device voltage measurement with respect to heating current while taking into account of the device temperature sensitive parameter and calculations. Thermal transient measurement involved the transient measurement of the device in cooling state after being heated for a period of time. Experimental results on the junction temperature of p-Ge IR emitter are presented. Excellent agreement between the results obtained via these 3 methods is found. It is proven to be suitable for junction temperature measurement of infrared emitters.