The interdiffusion and resistivity of Cu/Au, Cu/Co, Co/Au, and Cu/Co/Au thin‐film structures were studied, at temperatures ranging from 25 to 550 °C, using Rutherford backscattering spectroscopy, Auger analysis, and four‐point probe resistance measurements. Intermetallic phase formation was studied by x‐ray diffraction and changes in microstructure were analyzed by scanning electron microscopy. Interdiffusion of Cu and Au in the Cu/Au structure is observed at temperatures as low as 150 °C and is accompanied by an increase in resistivity. No significant reactions occur in the Cu/Co, Co/Au, and Cu/Co/Au thin‐film structures up to 400 °C, after which the resistivity increases. The very rapid increase in resistivity observed at 250 °C for the Cu/Au system and at 450 °C for Cu/Co/Au, is associated with structural changes in the films which result in large grains and the formation of AuCu, Cu3Au, and Cu3Au2compounds. The structural changes in the Cu/Co/Au system occur at a higher temperature because of the time needed for Cu and Au to diffuse through the Co barrier, which did not react significantly with either Au or Cu.