A buried ridge stripe (BRS) gain chip integrated with a fiber Bragg grating external cavity is fabricated for stable, single mode narrow-linewidth semiconductor laser with wavelength of 1.5 μm. The laser can realize single longitudinal mode output with the side-mode suppression ratio over 40 dB in the bias current tuning from 30 mA to 250 mA. The largest output power from fiber pigtail is larger than 10 mW. In the current tuning range, the linewidth is below 15.48 kHz and a minimum linewidth of 6.75 kHz is achieved. By using the beating-frequency method, the measured frequency fluctuation is 7.2×10-8/s. This compact and low cost narrow linewidth laser can be used as the optical source and the local oscillation source in the future 400 Gb/s communication systems.