Devices and methods for forming a device are presented. The method includes providing a substrate having at least a first region and a second region prepared with isolation regions. The first region is referred to as a chip guarding area and the second region defines a chip region of which at least one transistor is to be formed. The substrate includes a top surface layer, a support substrate and an insulator layer in between them. A transistor is formed in the second region and a substrate contact structure is formed in the first region. The substrate contact structure passes through at least the top surface layer, insulator layer and isolation region and contacts a doped region in the support substrate. The substrate contact structure is connected to at least one conductive line with a desired potential to prevent charging of the support substrate at system level.