The degradation of 1.3‐μm InP/InGaAsP light‐emitting diodes (LED’s) with misfit dislocations was investigated. Initially, the misfit dislocations were found to be present only in the p‐InP confining layer and they thus showed weak (∼1%) contrast in the electroluminescence (EL) image of the light‐emitting region. Without bias, no degradation of the LED’s was measured after 103 h at 200 °C. After 103 h at 20 °C and 8 kA/cm2, a previous study found that InP/InGaAsP LED’s containing misfit dislocations did not degrade. However, our study showed that the lifetime of the LED’s varied inversely with the third power of the current density. In the degraded LED’s, the misfit dislocations showed stronger (∼50%) contrast in the EL image, suggesting that they played a significant role in the device degradation. In these devices, misfit dislocations were found not only in the p‐InP confining layer but also in the light‐emitting region of the active layer. The degradation of InP/InGaAsP LED’s with misfit dislocations is thus consistent with the mechanism of nonradiative recombination enhanced growth of the misfit dislocations into the active layer. For our device structure, wafers with Δa/a≲0.05% lattice mismatch are free of misfit dislocations and thus ensure reliable device operation at high current densities.