Devices and methods of fabricating vertical nanowires on semiconductor devices are provided. One method includes: obtaining an intermediate semiconductor device having a substrate, a first insulator disposed above the substrate, a material layer over the first insulator, a second insulator above the material layer, and a first hardmask; etching a plurality of vertical trenches through the hardmask, the first and second insulators, and the material layer; growing, epitaxially, a set of silicon nanowires from a bottom surface of the plurality of vertical trenches; etching a first set of vertical trenches to expose the material layer; etching a second set of vertical trenches to the substrate; depositing an insulating spacer material on a set of sidewalls of the first and second set of vertical trenches; and forming contacts in the first and second set of vertical trenches.