High-temperature performance of a beam-expander (BEX) integrated laser was dramatically improved by reducing the current leakage in both longitudinal and lateral directions. Proton implantation into the BEX region and a reverse-mesa structure were combined to improve the high-temperature characteristics, A threshold current of 23.1 mA at 85 degrees C and a very high-characteristic temperature T-0 (25 degrees C-85 degrees C) of 74 K were achieved, Stable operation for over 3000 h under a 10-mW output power at 70 degrees C were confirmed.