A transistor includes substrate having an active region therein. The active region includes a recess therein having opposing sidewalls and a surface therebetween. A protrusion extends from the surface of the recess between the opposing sidewalls thereof. The transistor further includes a gate insulation layer on the protrusion in the recess, a gate electrode on the gate insulation layer in the recess, and source/drain regions in the active region on opposite sides of the gate electrode and adjacent to the opposing sidewalls of the recess. The gate electrode includes portions that extend into the recess between the protrusion and the opposing sidewalls of the recess. Related methods of fabrication are also discussed.