In an inventive MOS transistor having a source region, a drain region and a channel region, which are formed in a semiconductor layer of an SOI substrate, which has a semiconductor substrate below the semiconductor layer and an isolation layer between semiconductor layer and semiconductor substrate, the drain or source region is electrically connected to a backside contact on a side of the semiconductor substrate facing away from the isolation layer by a via running through the semiconductor substrate. The central idea of the present invention is to obtain an easy contactability of an MOS transistor without limitations in the application spectrum, by leading a via either from the source or the drain region across both the isolation layer and the semiconductor substrate to a backside contact, to be electrically connected to the same, since thereby the requirements of the material properties of the semiconductor substrates, such as doping and conductivity, are unnecessary or reduced.