A semiconductor device includes etching fins into a bulk substrate in an active region, the bulk substrate including an intermediate layer formed over a base layer and a first semiconductor layer formed over the intermediate layer such that the fins extend through the first semiconductor layer into the intermediate layer to form tapered bottom portions of the fins within the intermediate layer and vertical fin sidewalls of a semiconductor portions of the fins within the first semiconductor layer. A second semiconductor layer is formed around the tapered bottom portions below the semiconductor portions of the fins such that the second semiconductor layer covers the tapered bottom portions to form a top surface proximal to the semiconductor portions of the fins that is substantially parallel to a bottom surface of the top surface of the base layer. A gate structure is formed around the fins.