Semiconductor devices and fabrication methods thereof. The semiconductor device includes a semiconductor substrate with a body region of a first doping type. A gate structure is patterned on the semiconductor substrate. A single spacer is formed on a first sidewall of the gate structure. A body region of a first doping type is formed in the semiconductor substrate adjacent to a second sidewall of the gate structure. A source region of a second doping type is formed on the body region and having an edge aligned with the second sidewall of the gate structure. A drain region of the second doping type is formed on the semiconductor substrate and having an edge aligned with an exterior surface of the single sidewall.