A semiconductor structure comprises a first layer. The first layer comprises a first III-V semiconductor material. The semiconductor structure also comprises a second layer over the first layer. The second layer comprises a second III-V semiconductor material different from the first III-V semiconductor material. The semiconductor structure further comprises an insulating layer over the second layer. The insulating layer is patterned to expose a portion of the first layer. The exposed portion of the first layer comprises electrons of the second layer. The semiconductor structure additionally comprises an intermetallic compound over the exposed portion of the first layer.