A semiconductor device includes a gate structure, a first doped region, a second doped region, an isolation structure, an insulating layer and a field plate. The gate structure is located on a substrate. The first doped region and the second doped region are located at two sides of the gate structure. The isolation structure is located in the substrate between the first doped region and the second doped region, and is separated from the gate structure by a non-zero distance. The insulating layer extends continuously from a portion of a top surface of the gate structure to a portion of a top surface of the isolation structure. The field plate is located on the insulating layer and has the same potential as the gate structure.