On application of uniaxial pressure perpendicular to the junction, the threshold current of GaAs double‐heterostructure injection lasers at room temperature is observed to increase to a certain critical pressureP0, and then decrease with further increase in pressure. A flip of the polarization of laser light occurs atP0. This behavior can be explained using a model previously proposed to explain the reduction in threshold of homostructure GaAs lasers upon application of uniaxial pressure.