It is the purpose of the invention to provide a MOS transistor (20) which guarantees a voltage as high as possible, has a required area as small as possible and which enables the integration into integrated smart power circuits. It results there from as an object of the invention to form the edge structure of the transistors such that it certainly fulfils the requirements on high breakthrough voltages, a good isolation to the surrounding region and requires a minimum of surface on the silicon disc anyway. This is achieved with an elongated MOS power transistor having drain (30) and source (28) for high rated voltages above 100V, wherein the transistor comprises an isolating trench (22) in the edge area for preventing an early electrical breakthrough below the rated voltage. The trench is lined with an isolating material (70, 72), wherein the isolating trench terminates the circuit component.