Fabricating a semiconductor device includes receiving a substrate structure including a substrate. The substrate structure further includes a first bottom source/drain and a first fin formed on a vertical transistor portion of the substrate and a second bottom source/drain and a second fin formed on a varactor portion of the substrate. The substrate structure further includes a bottom spacer formed on the first bottom source/drain of the vertical transistor portion and the second bottom source/drain of the varactor portion. A mask is applied to the portion of the bottom spacer formed on the first bottom source/drain. The portion of the bottom spacer formed on the second bottom source/drain of the varactor portion is removed. The mask is removed from the portion of the bottom spacer formed on the first bottom source/drain. A gate oxide is deposited on the vertical transistor portion and the varactor portion.