Five types of commercial production thermal barrier coatings (TBCs) were non-destructively examined as a function of furnace thermal cycling using electrochemical impedance spectroscopy (EIS). Impedance response was acquired at room temperature and analyzed with AC equivalent circuits based on the multi-layered structure and micro-constituents of TBCs. Impedance of the TBC system increased due to an increase in the resistance (or decrease in capacitance) of the Yttria Stabilized Zirconia (YSZ) topcoat and thermally grown oxide (TGO) initially with thermal cycling. Prior to failure of TBCs, the resistance of YSZ and TGO was similar to those at as-received condition. The exposed metallic bond coat surface on the fracture surface, which provides conduction readily through electrolyte contact, was related to the abrupt and large increase in the capacitance of YSZ and TGO. These correlated observations from EIS, microstructure and fracture surface are discussed quantitatively with phenomenological descriptions of electrochemical impedance.