Transistors and methods of forming the same include forming a semiconductor fin from a first material on dielectric layer. Material is etched away from the dielectric layer directly underneath a channel region of the semiconductor fin, with the semiconductor fin still being supported by the dielectric layer in a source and drain region. A gate stack is formed around the channel region of the semiconductor fin, with a portion of the gate stack underneath the semiconductor fin being larger than a portion of the gate stack above the semiconductor fin.