A method and structure providing a high-voltage transistor (HVT) including a gate dielectric, where at least part of the gate dielectric is provided within a trench disposed within a substrate. In some aspects, a gate oxide thickness may be controlled by way of a trench depth. By providing the HVT with a gate dielectric formed within a trench, embodiments of the present disclosure provide for the top gate stack surface of the HVT and the top gate stack surface of a low-voltage transistor (LVT), formed on the same substrate, to be substantially co-planar with each other, while providing a thick gate oxide for the HVTs. Further, because the top gate stack surface of HVT and the top gate stack surface of the LVT are substantially co-planar with each other, over polishing of the HVT gate stack can be avoided.