Disclosed are methods for forming fins. In an example embodiment, a method includes providing a substrate that includes at least two elongated structures separated by an isolation region. Each elongated structure comprises a semiconductor alloy of a first semiconductor material and a second semiconductor material, and a relaxed portion of the elongated structure includes the semiconductor alloy in a relaxed and substantially defect-free condition. The method further includes subjecting the substrate to a condensation-oxidation, such that each elongated structure forms a fin and an oxide layer. The fin includes a fin base portion formed of the semiconductor alloy and a fin top portion of the first semiconductor material in a strained condition. The fin top portion is formed by condensation of the first semiconductor material. The oxide layer includes an oxide of the second semiconductor material. The method further includes removing at least some of the oxide layer.