Embodiments of present invention provide a method of forming a transistor structure. The method includes forming a set of vertical fins on top of a substrate; forming a conformal spacer lining the set of vertical fins and the substrate; forming sidewall spacers next to vertical portions of the conformal spacer; removing portions of the conformal spacer on top of the substrate and between the sidewall spacers; indenting the conformal spacer vertically between the sidewall spacers and the substrate to create openings; forming bottom spacers in the openings; and forming a shallow-trench-isolation (STI) structure between the bottom spacers. A structure formed thereby is also provided.