An LDMOS includes a substrate. A lateral direction is parallel to a top surface of the substrate, and a metal gate is disposed on the substrate. The metal gate includes a first side, a second side and a bottom. The first side and the second side are opposite to each other. A source is disposed in the substrate and at the first side, and a drain is disposed in the substrate at the second side. A composite structure covers the first side, the second side and the bottom. The composite structure extends along the lateral direction from the second side to the drain. The composite structure includes a high dielectric material layer, a first work function layer and a second work function layer.

A method of forming a semiconductor device includes forming a first metal material lining a trench in a semiconductor substrate at a first temperature. The method further includes forming a second metal material lining the first metal material at a second temperature higher than the first temperature. The method further includes performing an annealing process to the first and second metal materials.

A method includes providing a structure. The structure includes a stack of bottom channel layers, a stack of top channel layers disposed over the stack of bottom channel layers, an isolation feature sandwiched by the stack of bottom channel layers and the stack of bottom channel layers, and a first work function metal (WFM) layer wrapping around each of the bottom channel layers. The method further includes forming a second WFM layer wrapping around each of the top channel layers, forming a passivation layer on the second WFM layer by performing a gas treatment to the structure, and forming a metal fill layer over the passivation layer.