One illustrative method disclosed herein includes forming a plurality of trenches in a semiconductor substrate to thereby define an initial fin structure, forming sidewall spacers adjacent the initial fin structure, wherein the spacers cover a first portion of the initial fin structure and expose a second a portion of the initial fin structure, performing a doping process to form N-type doped regions in at least the exposed portion of the initial fin structure, and performing an etching process to remove at least a portion of the doped regions and thereby define a final fin structure that is vertically spaced apart from the substrate.