This letter investigates the gain medium properties in II–VI blue‐green quantum well semiconductor lasers, including band structure and carrier interactions in the electron‐hole plasma are found to be significantly more important than in infrared III–V lasers. In particular, the interband Coulombic enhancement of the optical transitions, together with a band gap renormalization result in an increase in gain and a reduction in the antiguiding or linewidth enhancement factor. ©1995 American Institute of Physics.