A semiconductor structure comprises a drift region of a first conductivity type in a semiconductor region. A well region of a second conductivity type is over the drift region. A source region of the first conductivity type is in an upper portion of the well region. A heavy body region of the second conductivity type extends in the well region. The heavy body region has a higher doping concentration than the well region. A first diffusion barrier region at least partially surrounds the heavy body region. A gate electrode is insulated from the semiconductor region by a gate dielectric.