Provided is a ridge waveguide type semiconductor laser device in which
fundamental transverse mode operation is stabilized and unstable jumps of
a longitudinal mode (oscillation wavelength) never occur even with use of
high optical output of 300 mW or more. The semiconductor laser device has
a stacked structure composed of a substrate and layers thereon. The layers
include a lower cladding layer, lower optical confinement layer, active
layer, upper optical confinement layer, and upper cladding layer, which
are built up in the order named. A ridge is formed on the upper cladding
layer. The width (W) of the bottom ridge portion of the ridge ranges from
2.5 .mu.m to 5.0 .mu.m, and the distance from the bottom ridge portion to
an active layer is adjusted to a value higher than 0.5 .mu.m and not
higher than 0.8 .mu.m.
