Effects of the high-reflectivity mirrors on the performance of (GaAl)As diode lasers are investigated by using a laser diode model. An optimum value for the mirror reflectivity is obtained by using a figure of merit which reflects low threshold and high slope efficiency. An optimum reflectivity value

is obtained for a laser with a cavity length

m and an internal loss coefficient

cm
-1. A higher internal photon flux density relative to the output photon flux density is shown to occur with the high-reflectivity mirror. High-reflectivity mirrors are shown to reduce optical feedback effect from external devices and the lowered threshold value to reduce the thermal effects on the modulation characteristics and the degradation.