We report the fabrication of KCu7S₄/CuxO/Au devices with interfacial CuxO layers of different thicknesses through the spontaneous oxidation of Cu film during deposition. Deposition was conducted with an electron-beam evaporation system under the deposition rate and the chamber pressure of 0.1 Å s-1 and 9.8×10-3 Pa, respectively. X-ray diffraction and X-ray photoelectron spectroscopy characterizations reveal that the interfacial CuxO layers mostly comprise Cu₂O and CuO. Electrical characterization reveals that the devices exhibit remarkably thickness-dependent resistive switching behavior. After undergoing an electroforming process under a high compliant current of 1000 μA, the KCu7S₄/16 nm CuxO/Au device exhibits stable bipolar resistive switching behavior with the set voltage of 0.58 V and reset voltage of -0.21 V, whereas the KCu7S₄/32 nm CuxO/Au device only shows a hysteresis loop in the forward voltage regime. These findings are ascribed to the existence of high-insulation CuO, which is difficult to be softly broken down. Therefore, the depositional condition of Cu film and the thickness of the interfacial layer should be appropriately controlled for the effective performance of devices with Cu electrodes. The results may also provide guidance for the improvement of the performance and stability of Cu-based nonvolatile memory devices.