The present disclosure relates to semiconductor structures and, more particularly, to vertically stacked field effect transistors and methods of manufacture. The structure includes: at least one lower gate structure on a bottom of a trench formed in substrate material; insulator material partially filling trench and over the at least one lower gate structure; an epitaxial material on the insulator material and isolated from sidewalls of the trench; and at least one upper gate structure stacked vertically above the at least one lower gate structure and located on the epitaxial material.