Field effect transistors including source/drain regions extending beneath pillars

Field effect transistors include a substrate and a pillar that extends away from the substrate. The pillar includes a base adjacent the substrate, a top remote from the substrate, and a sidewall that extends between the base and the top. An insulated gate is provided on the sidewall. A first source/drain region is provided in the substrate beneath the pillar and adjacent the insulated gate. A second source/drain region that is heavily doped compared to the first source/drain region, is provided in the substrate beneath the pillar and remote from the insulated gate. The pillar may be an I-shaped pillar that is narrower between the base and the top compared to adjacent the base and the top, such that the sidewall includes a recessed portion between the base and the top.