A vertical transistor includes a semiconductor wafer having a plurality of pillar structures extending orthogonally from the semiconductor wafer. Each pillar structure forms a vertical pillar transistor having a top surface and a side surface orthogonal to the top surface. Then a hardening ion species is implanted into the vertical pillar transistor top surface. Then the vertical pillar transistor side surface is oxidized to form a side surface oxide layer. The side surface oxide layer is removed to form vertical pillar transistor having rounded side surfaces.