The present invention relates to transistor devices having a trough channel structure through which electrical current flows and methods for making the same. A transistor device having a semiconductor trough structure comprises a semiconductor substrate of a first conductivity type having a top surface; a semiconductor trough protruded from the top surface of the substrate along a first direction and having two top surfaces, two outer lateral surfaces, and an inner surface; a layer of isolation insulator disposed on the substrate and abutting the outer lateral surfaces of the semiconductor trough; a gate dielectric layer lining the inner surface and the top surfaces of the semiconductor trough; and a gate electrode disposed on top of the isolation insulator and extending over and filling the semiconductor trough with the gate dielectric layer interposed therebetween. The gate electrode extends along a second direction not parallel to the first direction provided in the semiconductor trough. Regions of the semiconductor trough not directly beneath the gate electrode have a second conductivity type opposite to the first conductivity type provided in the substrate.