The threshold voltage of parasitic transistors formed at corners of shallow trench isolation regions is increased and mobility decreased by employing a high-K dielectric material. Embodiments include STI regions comprising a liner of a high-K dielectric material extending proximate trench corners. Embodiments also include STI regions having a recess formed in the trench, wherein the recess contains a high-K dielectric material, in the form of a layer or spacer, extending proximate trench corners.