A structural alternative to retro doping to reduce transistor leakage is provided by providing a liner in a trench, undercutting a conduction channel region in an active semiconductor layer, etching a side, corner and/or bottom of the conduction channel where the undercut exposes semiconductor material in the active layer and replacing the removed portion of the conduction channel with insulator. This shaping of the conduction channel increases the distance to adjacent circuit elements which, if charged, could otherwise induce a voltage and cause a change in back-channel threshold in regions of the conduction channel and narrows and reduces cross-sectional area of the channel where the conduction in the channel is not well-controlled; both of which effects significantly reduce leakage of the transistor.