A silicon-carbon alloy layer and a silicon-germanium alloy layer are sequentially formed on a silicon-containing substrate with epitaxial alignment. Trenches are formed in the silicon-germanium alloy layer by an anisotropic etch employing a patterned hard mask layer as an etch mask and the silicon-carbon alloy layer as an etch stop layer. Fin-containing semiconductor material portions are formed on a bottom surface and sidewalls of each trench with epitaxial alignment with the silicon-germanium alloy layer and the silicon-carbon alloy layer. The hard mask layer and the silicon-germanium alloy layer are removed, and an oxygen-impermeable spacer is formed on sidewalls of each fin-containing semiconductor material portion. Physically exposed semiconductor portions are converted into semiconductor oxide portions, and the oxygen-impermeable spacers are removed. The remaining portions of the fin-containing semiconductor portions include semiconductor fins, which can be employed to form semiconductor devices.