A group III chalcogenide layer for interfacing a high-k dielectric to a III-V semiconductor surface and methods of forming the same. A III-V QWFET includes a gate stack which comprises a high-K gate dielectric layer disposed on an interfacial layer comprising a group III chalcogenide. In an embodiment, a III-V semiconductor surface comprising a native oxide is sequentially exposed to TMA and H2S provided in an ALD process to remove substantially all the native oxide and form an Al2S3 layer on the semiconductor surface.