A semiconductor structure is provided. The semiconductor structure includes a substrate, at least a first N-type germanium (Ge) structure and at least a first P-type Ge structure. The first N-type Ge structure is formed on the substrate and has two end parts and at least a first central part bonded between the two end parts thereof. The first central part is floated over the substrate, and a side surface of the first central part is a {111} Ge crystallographic surface. The first P-type Ge structure is formed on the substrate and has two end parts and at least a second central part bonded between the two end parts thereof. The side surface of the second central part is a {110} Ge crystallographic surface.