The present disclosure describes a method for forming ultra-thin fins with a tapered bottom profile for improved structural rigidity and gate control characteristics. The method includes forming a fin structure that includes an epitaxial layer portion and a doped region portion surrounded by an isolation region so that a top section of the epitaxial layer portion is above the isolation region. The method also includes depositing a silicon-based layer on the top portion of the epitaxial layer above the isolation region and annealing the silicon-based layer to reflow the silicon-based layer. The method further includes etching the silicon-based layer and the fin structure above the isolation region to form a first bottom tapered profile in the fin structure above the isolation region and annealing the fin structure to form a second bottom tapered profile below the first bottom tapered profile and above the isolation region.