Structures for a field-effect transistor and methods of forming a structure for a field-effect transistor. A semiconductor substrate includes a first region, a second region, and a first source/drain region in the first region. A semiconductor fin is located over the second region of the semiconductor substrate. The semiconductor fin extends laterally along a longitudinal axis to connect to the first region of the semiconductor substrate. The structure includes a second source/drain region including an epitaxial semiconductor layer coupled to the first semiconductor fin, and a gate structure that extends over the semiconductor fin. The gate structure includes a first sidewall and a second sidewall opposite the first sidewall, the first source/drain region is positioned adjacent to the first sidewall of the gate structure, and the second source/drain region is positioned adjacent to the second sidewall of the gate structure.