A high quality single crystal substrate and a method of fabricating the same are provided. The method of fabricating a single crystal substrate includes: forming an insulator on a substrate; forming a window in the insulator, the window exposing a portion of the substrate; forming an epitaxial growth silicon or germanium seed layer on the portion of the substrate exposed through the window; depositing a silicon or germanium material layer, which are crystallization target material layers, on the epitaxial growth silicon 6r germanium seed layer and the insulator; and crystallizing the crystallization target material layer by melting and cooling the crystallization target material layer.