Inthispaper,wepresentedinvestigationonthemeasurementofthermalimpedanceofphasecontrolthyristoranditsexperimentalresults.Thermalimpedanceiscomposedofthermalresistanceandheatcapacity.Thermalresistancewasdrivedfromtheresponsecharacteristiconunitsteptothermalsystemashighpowerthyristor,IPMandpowerdevice.ThethermalmodelofthemisdescribedasadiscreteR(z)functionandthecorrespondingFoster.orCauelladdernetworkmodel.Toconfirmthismeasurement,withusingWestcodeandDynexthyristorasasample,thisonewasverifiedwith10$\%$errorascomparedwiththethesedata-sheet.