In this paper we examine the effect of coupling between the wells on the differential gain. We find, as for the gain peak, the differential gain at the gain peak is not a monotonic function of the barrier thickness. For relatively thick barriers inclusion of coupling reduces the differential gain but as the barrier gets thinner the differential gain can be significantly enhanced or suppressed. We also compare our calculations with those for single quantum well to show how the enhancement in differential gain in the multi quantum well laser, due to reduced state filling and higher modal gain is affected by well coupling. Without losing generality, the model assumes the quantum well region to be electric field free. Numerical examples are presented for a GaAs/Al0.2Ga0.8As double quantum well system. ©1995 American Institute of Physics.