A method of manufacturing a semiconductor device is provided including providing an SOI substrate comprising a semiconductor bulk substrate, a buried insulation layer and a semiconductor layer, forming a shallow trench isolation in the SOI substrate, forming a FET in and over the SOI substrate, and forming a contact to a source or drain region of the FET that is positioned adjacent to the source or drain region, wherein forming the shallow trench isolation includes forming a trench in the SOI substrate, filling a lower portion of the trench with a first dielectric layer, forming a buffer layer over the first dielectric material layer, the buffer layer having a material different from a material of the first dielectric layer, and forming a second dielectric layer over the buffer layer and of a material different from the material of the buffer layer.