The present disclosure provides a test structure which includes an SOI substrate having an active semiconductor layer, a buried insulating material layer, and a base substrate, wherein the active semiconductor layer is formed on the buried insulating material layer, which, in turn, is formed on the base substrate. The test structure further includes a contact which is formed on the active semiconductor layer and electrically coupled to the active semiconductor layer. Herein, the contact has a tip portion extending through the active semiconductor layer into the buried insulating material layer.