AlxGa1-xAs laser diodes tested in vacuum (10-6 Torr) at a -20 °C heat sink temperature (Tj ∼0 °C) and with an average drive current of 160 mA for one set of diodes (test 1), and 190 mA for another set (test 2), were found to have small decreases in output power due to facet degradation, heat sink degradation, and bulk degradation. Analyses described in this paper show that the degradation mechanism causing the largest decrease in output power was gradual bulk degradation due to arsenic (As) out‐diffusion from the active region. The arsenic out‐diffusion was most likely caused by a processing anomaly. The data further indicate that the As out‐diffusion increases with current. The results from this research can be used to identify a possible cause and accelerating stress of long‐term gradual degradation. It was also observed that defects created by this degradation mechanism (suspected to be As vacancies) caused little change in the forward voltage at 1 mA.