A semiconductor structure includes a substrate, an insulating layer disposed on the substrate, an active layer disposed on the insulating layer, a plurality of isolation structures in the active layer to define a first device region and a non-device region of the active layer, a first semiconductor device formed on the first device region of the active layer, and a charge trap structure extending through the non-device region of the active layer. In a plane view, the charge trap structure and the non-device region form concentric closed ring surrounding the first device region.