A method of making a semiconductor device includes forming an intermediate structure including second semiconductor fin portions above a first semiconductor layer, and top first semiconductor fin portions extending from respective ones of the second semiconductor fin portions. The second semiconductor fin portions are selectively etchable with respect to the top first semiconductor fin portions. A dummy gate is on the intermediate structure. The second semiconductor fin portions are selectively etched to define bottom openings under respective ones of the top first semiconductor fin portions. The bottom openings are filled with a dielectric material.