A polarization-dependent rate-equation model on polarization-dependent emission characteristics of internally strained 1.3-μm InGaAsP/InP semiconductor lasers is presented. Among the rate-equation parameters, the polarization-dependent gain and gain-saturation coefficients are calculated using the density-matrix approach and the confinement factors and loss coefficients are related to the waveguide structure. Numerical simulations show that anomalous polarization-dependent emission characteristics can occur when the internal stress is in the 108-dyn/cm2 order of magnitude. Various types of emission characteristics from measurements and simulations are shown and the conditions for these emission characteristics are discussed. Single-polarization emission and two-polarization switching, including polarization bistability, are found in the low-stress regime and two-polarization coexisting characteristics are found in the high-stress regime.