The influence of active layer thickness and p-type dopants for a cladding layer on laser reliability was investigated using GaAlAs modified channeled substrate planar (MCSP) lasers operating at around 780 nm. The proportion of short-lived lasers increases abruptly when the active layer thickness becomes less than 0.04 µm. This phenomenon is attributed to the abrupt increase of carrier density in the active layer at the lasing threshold. Zinc was found to be superior to germanium as a p-type dopant of the cladding layer in terms both of the temperature dependence of the threshold current, and of laser reliability. A cumulative failure rate as low as 2.7% over 2000 hour operation at 70°C was achieved for MCSP lasers having an active layer thickness and Zn concentration of the cladding layer that were optimized.