Abstract: A high voltage metal oxide semiconductor includes a doped substrate, two first isolation structures, a gate structure, a source region, a drain region, two second isolation structures, and two drift regions. The two first isolation structures are respectively disposed in the doped substrate. The gate structure is disposed between parts of the two first isolation structures on the doped substrate. The source region and the drain region are respectively disposed beside one side of each of the two first isolation structures in the doped substrate. The top surface of the second isolation structure is smaller than the bottom surface of the first isolation structure. The two drift regions are respectively disposed in the doped substrate, enclosing the source region and the drain region, the two first isolation structures and the second isolation structures.