SOI semiconductor components and methods for their fabrication are provided wherein the SOI semiconductor components include an MOS transistor in the supporting semiconductor substrate. In accordance with one embodiment the component comprises a semiconductor on insulator (SOI) substrate having a first semiconductor layer, a layer of insulator on the first semiconductor layer, and a second semiconductor layer overlying the layer of insulator. The component includes source and drain regions of first conductivity type and first doping concentration in the first semiconductor layer. A channel region of second conductivity type is defined between the source and drain regions. A gate insulator and gate electrode overlie the channel region. A drift region of first conductivity type is located between the channel region and the drain region, the drift region having a second doping concentration less than the first doping concentration of first conductivity determining dopant.