In this article, the properties of the Ge/Bi 2 O 3 interfaces as microwave cavities are reported and discussed. The interface is composed of monoclinic Bi 2 O 3 films grown onto polycrystalline cubic Ge substrate. It is observed that consistent with the theoretical design of the energy band diagram, the experimental current-voltage characteristics of the Yb/Ge/Bi 2 O 3 /C hybrid device structure exhibits electronic switching property. In addition, the capacitance, resistance and microwave cutoff frequency spectral analysis in the frequency domain of 0.01-1.50 GHz revealed a frequency dependent tunability of the device. Moreover, while the Yb/Bi 2 O 3 /C interface displays negative capacitance effect, the Yb/ Ge/Bi 2 O 3 /C interfaces are also found to have the ability of altering the resistance up to three orders of magnitude. Such property allowed reaching a cut off frequency up to 116 GHz. The electronic features of the device indicated that the Ge/Bi 2 O 3 interfaces are attractive for production of negative capacitance field effect transistors and band pass/reject filters.