A novel step high-k metal–oxide–semiconductor field-effect transistor (step HK-MOSFET) is designed with the step high-k insulator based on the HK-MOSFET concept for the first time. In the off-state, the step HK insulator enhances the lateral field component in the drift region due to the new electric field peak, which increases the depletion of the drift region and leading to the low specific on-resistance (R _{on, sp}) of step HK-MOSFET compared with the conventional HK-MOSFET. Meanwhile, the various thicknesses of the HK insulator modulates the vertical electric field distribution in the drift region, which increases the breakdown voltage (BV) of step HK-MOSFET compared with the conventional vertical double diffused MOSFET and HK-MOSFET. The results show that the simulated BV of step HK-MOSFET is increased from 639 V of the conventional HK-MOSFET to 736 V with the same drift region length of 42 μm or decreased the requirement of permittivity for the HK region to 120 ɛ ₀ from 230 ɛ ₀ with the same BV of 600 V.