Abstract: A metal oxide semiconductor field transistor including a gate electrode, a gate dielectric layer, a source region, a drain region, and a top doped region are provided. The drain region of a first conductivity type is located in a substrate. The source region of the first conductivity type is located in the substrate and surrounded the drain region. The gate electrode is located above the substrate between the source region and the drain region. The gate dielectric layer is located between the gate electrode and the substrate. The top doped region of a second conductivity type is located in the substrate between the gate electrode and the drain region. The top doped region includes at least three regions. Each of the three regions has a dopant concentration gradient and a concentration gradually decreased from a region adjacent the gate electrode to a region adjacent the drain region.