We have investigated the thermally induced tensile strain in Ge-on-Si for use in optical sources of interconnection systems. Epitaxial Ge layers were grown using a two-step hetero-epitaxy at low and high temperatures. The as-grown Ge-on-Si was then annealed for direct bandgap conversion. A tensile strain of 0.06% in the as-grown Ge increased to 0.31% after annealing at 850 degrees C. As the thermal budget of this post-growth anneal was increased, the tensile strain of relaxed Ge-on-Si also increases and a Si-Ge alloy forms. Physical characterization indicates a tunable tensile stain in Ge-on-Si can be realized using post-growth annealing, which will allow for a wide range of frequencies in optical interconnections.