The fabrication process, the analysis of the waveguiding property, and the lasing characteristics of a separated multiclad-layer (SML) stripe-geometry laser for a 0.8 μm wavelength are described. The SML stripe geometry enables us to grow at 820°C a flat active layer without deformation of the shape of the grow by melt-etching. The analysis shows that the built-in waveguide is the effective refractive index step waveguide, in contrast to the loss step waveguide of the CSP laser, and we can fabricate a laser with small stripewidth. The fundamental transverse and longitudinal single-mode lasing were obtained with CW threshold current of 45-70 mA for the stripewidth m. The damped relaxation oscillation and the small spectral broadening when modulated by 400 Mbits/s RZ random pulses were obtained. A small increase rate of the driving current when operated at 50°C with 5 mW/facet output was confirmed.