The fabrication of 250 Å thick, undoped, single crystal silicon on insulator by lateral solid phase epitaxial growth from amorphous silicon on oxide patterned (001) silicon substrates is reported. Amorphous silicon was grown by low pressure chemical vapor deposition at 525°C using disilane. Annealing at temperatures between 540 and 570°C is used to accomplish the lateral epitaxial growth. The process makes use of a Si/Si1-xGex/Si stacked structure and selective etching. The thin Si1-xGex etch stop layer (x=0.2) is deposited in the amorphous phase and crystallized simultaneously with the Si layers. The lateral growth distance of the epitaxial region was 2.5 μm from the substrate seed window. This represents a final lateral to vertical aspect ratio of 100:1 for the single crystal silicon over oxide regions after selective etching of the top sacrificial Si layer. The effects of Ge incorporation on the lateral epitaxial growth process are also discussed. The lateral epitaxial growth rate of 20% Ge alloys is enhanced by roughly a factor of three compared to the rate of Si films at an anneal temperature of 555°C. Increased random nucleation rates associated with Ge alloy films are shown to be an important consideration when employing Si1-xGex to enhance lateral growth or as an etch stop layer.