It is shown that the unique properties of strained‐layer quantum well lasers can be identified by measuring the relaxation oscillation frequency as a function of optical gain. These measurements are insensitive to effects due to nonradiative recombinations and leakage currents, which can mask the beneficial effects in terms of a lower threshold current due to a reduced hole mass in strained quantum wells. The conclusion, both theoretically and experimentally, is that strained‐layer quantum well lasers have a higher differential gain but saturate at a lower gain level as compared to regular quantum well lasers. As a consequence, for a strained single quantum well, slightly higher relaxation oscillation frequency results, but only for certain limited ranges of device parameters. A multiple strained‐layer quantum well can in theory take better advantage of the higher differential gain.