An extremely small minimum scaled Metal-Oxide-Semiconductor, MOS, transistor is manufactured by forming a trench in a semiconductor substrate, forming a gate in the trench, and then forming source and drain regions. The source and drain regions may be diffused into the semiconductor substrate and annealed to drive the diffusions around the trench corners, thus forming the transistor channel. This improves punchthrough resistance of the transistor while yielding an extremely small gate channel. The diffusion concentration will be larger near the surface of the semiconductor substrate and smaller near the plane of the gate channel underneath the trench bottom. The trench corners have the effect of serving as a line source of dopant for diffusion under the trench such that the doping profile is the same along a radius of a cylindrical junction, thus keeping the minimum diffusion separation at the channel surface.