A method for making a semiconductor device may include forming a first semiconductor layer on a substrate comprising a first semiconductor material, forming a second semiconductor layer on the first semiconductor layer comprising a second semiconductor material, and forming mask regions on the second semiconductor layer and etching through the first and second semiconductor layers to define a plurality of spaced apart pillars on the substrate. The method may further include forming an oxide layer laterally surrounding the pillars and mask regions, and removing the mask regions and forming inner spacers on laterally adjacent corresponding oxide layer portions atop each pillar. The method may additionally include etching through the second semiconductor layer between respective inner spacers to define a pair of semiconductor fins of the second semiconductor material from each pillar, and removing the inner spacers and forming an oxide beneath each semiconductor fin.