Devices and methods are provided for fabricating vertical field-effect transistor devices for monolithic three-dimensional semiconductor integrated circuit devices. A semiconductor structure is formed to include a substrate and a stack of layers formed on the substrate including a first active semiconductor layer, an insulating layer, and a second active semiconductor layer. A vertical fin structure is formed by patterning the first and second active semiconductor layers and the insulating layer, wherein the vertical fin structure includes first and second vertical semiconductor fins, and an insulating fin spacer disposed between the first and second vertical semiconductor fins. The first and second vertical semiconductor fins are utilized to fabricate first and second vertical field-effect transistor devices on first and second device layers of a monolithic three-dimensional semiconductor integrated circuit device.