Aging tests of InGaAsP/InP V‐grooved substrate buried heterostructure lasers have performed. The cw threshold current of these lasers is around 20 mA at 25 °C. The laser are tested at 10, 50, and 70 °C with a constant optical power of 5 mW/facet and are still operating at over 5000 h with only a slight increase in the driving current. The far‐field pattern and lasing spectrum do not change appreciably during aging, and self‐pulsation is not observed after aging.