Room‐temperature gain coupled distributed feedback (GC‐DFB) lasers have been realized by implantation induced intermixing in the GaAs/AlGaAs material system. The implantation dose has been systematically varied to realize GC‐DFB lasers with different gain coupling coefficients due to different band‐gap modulation of the active quantum wells. It is demonstrated that a band‐gap modulation of 7 meV is sufficient to achieve a high single mode yield at room temperature. The results are discussed on the basis of calculations with the optical matrix theory. ©1995 American Institute of Physics.