We have studied the microdefect induced degradation mode in long-lifetime blue-green laser diodes (LDs) and light emitting diodes (LEDs) based on II-VI wide bandgap semiconductors. Microscopic deep defect centers in the LDs and LEDs are detected using mainly DLTS technique, coupled with ICTS methods. It is evidenced that a slow-mode degradation, commonly observed in dislocation-free LD devices, is caused by the generation and enhancement of microscopic deep centers during the device aging process. One possible degradation mechanism with a "carrier removal effect" is presented.