The present disclosure relates to semiconductor devices, and more particularly, to high voltage extended drain MOSFET (EDMOS) devices in a high-k metal gate (HKMG) and methods of manufacture. A structure of the present disclosure includes a plurality of extended drain MOSFET (EDMOS) devices on a high voltage well with a split-gate dielectric material including a first gate dielectric material and a second gate dielectric material, the second gate dielectric material including a thinner thickness than the first gate dielectric material, and a high-k dielectric material on the split-gate dielectric material.