A semiconductor structure includes a SOI/BOX semiconductor substrate, a device, a deep trench, a silicon layer, and a dielectric layer. The deep trench is adjacent to the device and extends through a shallow trench isolation layer within the SOI layer and the BOX layer and into the base semiconductor substrate. The silicon layer is disposed within a lower portion of the deep trench. The silicon layer has a top surface height substantially the same as or lower than a top surface height of the base semiconductor substrate. The dielectric layer is disposed within the deep trench and on the silicon layer. The deep trench can be formed before or after formation of an interlayer dielectric.