A low-cost method to reduce the threading dislocations density (TDD) in relaxed germanium (Ge) epilayers grown on silicon (Si) substrates is presented. Ge/Si substrate was treated with post epitaxial process to create a region with a high density of nano-voids. The nano-voids are formed by a selective electrochemical porosification through dislocations followed by thermal annealing which act as a free surface for inhibiting dislocation propagation. The TD density is reduced significantly which will be crucial in cutting manufacturing costs of III-V multi-junction solar cells, if the bulk Ge substrates can be replaced with our engineered substrate.