A method of fabricating silicon (Si) and silicon germanium (SiGe) fins is described. The method includes forming at least two Si fins on a buried oxide (BOX) layer disposed on a substrate, at least one Si fin being formed in a first region and at least one Si fin being formed in a second region, the at least one Si fin in the second region being thinner than the at least one Si fin in the first region. The method also includes depositing an oxide mask over the first region, epitaxially growing an SiGe layer on the at least one Si fin in the second region, and performing a thermal annealing process to drive Ge from the SiGe layer into the at least one Si fin in the second region to form at least one SiGe fin in the second region.