Memristors exhibit very promising features such as nonvolatility and small area. Several types of memristors have been developed in the last decade using different materials along with physical models explaining their behaviors. In this paper, we modify a previously published model to account for a trapezoidal electron tunneling barrier rather than a zero field or constant potential barrier. The model is verified against experimental data showing better agreement. We then perform a study to find out the effect of different memristors parameters on its I–V characteristics and how to shape the characteristics to fit the applications. Finally, we provide a SPICE model which takes into account the tunneling capacitance and clarify that any fabricated memristor has, inherently, a memcapacitor in parallel. The dominant element may be the memristor or the memcapacitor depending on the frequency of operation.