Device lifetime has been improved to over 100 h by reducing dark-spot density (DSD) to less than 3 x 10(3) cm(-2). The lifetime of II-VI laser diodes is no longer limited by a rapid degradation but by gradual degradation due to microscopic point defects. Lifetime has been significantly improved up to similar to 500 h at 20 degrees C under CW operation with LDs grown in Se-rich conditions for the active layer. If we know the growth-condition dependence of degradation behaviors, it may be possible to improve the reliability of ZnSe-based LDs, ZnSe-based LDs are bring developed for applications such as display systems and printing systems utilizing their purr green emission,