We examine a Kerr phase gate in a semiconductor quantum well structure based on the tunnelling interference effect. We show that there exist a specific signal field detuning, at which the absorption/amplification of the probe field will be eliminated
with the increase of the tunnelling interference. Simultaneously, the probe field will acquire a -pi phase shift at the exit of the medium. We demonstrate with numerical simulations that a complete 180^circ phase rotation for the probe field at the exit of the medium is achieved, which may result in many applications in information science and telecommunication.
