A 1.3‐&mgr;m GaInAsP/InP buried crescent laser on ap‐type InP substrate was demonstrated. An active region width narrower than 1.5 &mgr;m was achieved with good controllability and reproducibility using the newly introduced reactive ion beam etching technique for the etching process. Stable fundamental transverse mode operation with low threshold currents of 15–25 mA was obtained. Less than 5% degradation in threshold current at 50 °C was achieved with a constant driving current of 150 mA at 70 °C for 100 h.