A scheme of a weak optical switch in GaAs-AlGaAs asymmetric coupled quantum wells is proposed. The effect of dephasing rate γ 21 on the switch is analysized. The optical switch is induced by Fano interference in coherent effects between inter subbands in superlattices. This weak semiconductor switch is more practical than that of atomic media due to its flexibility for choosing materials and structure dimensions of the utilized heterostructures. This is also a method of controlling one beam by another in semiconductor.