A semiconductor structure is disclosed. The semiconductor structure includes a first layer. A second layer is disposed on the first layer and different from the first layer in composition. An interface is between the first layer and the second layer. A third layer is disposed on the second layer. A gate is disposed on the third layer. A source feature and a drain feature are disposed on opposite sides of the gate. Each of the source feature and the drain feature includes a corresponding metal feature at least partially embedded in the second and the third layer. A corresponding intermetallic compound underlies each metal feature. Each intermetallic compound contacts a carrier channel located at the interface.