A power MOS transistor comprises a drain region, a trench gate, a source region, a well region, a deep well region and a substrate region. The drain region has a doping region of a first conductivity type connected to a drain electrode. The trench gate has an insulating layer and extends into the drain region. The source region has a doping region of the first conductivity type connected to a source electrode. The well region is doped with a second conductivity type, formed under the source region, and connected to the source electrode. The deep well region is doped with the first conductivity type and is formed under the drain region and the well region. The substrate region is doped with the second conductivity type and is formed under the deep well region. The drain region is formed at one side of the trench gate and the source region is formed at the opposing side of the trench gate such that the trench gate laterally connects the source region and the drain region.