A vertical power MOSFET with an interdigitated drift region using high-$k$ (Hk) insulator (Hk-MOSFET) is studied. Due to the fact that most of the electric displacement lines produced by the charges of the depleted drift region under reverse bias are through the Hk insulator, much heavier doping concentration can be used in the drift region when comparing with a conventional MOSFET with the same breakdown voltage. It is shown that the specific on-resistance of the Hk-MOSFET is comparable to that of the superjunction MOSFET (SJ-MOSFET) with the same breakdown voltage. The turn-on and turn-off times are found to be little longer than those of the conventional MOSFET and the SJ-MOSFET. The theoretical results of the electrical characteristics are in good agreement with the results from numerical simulations.