High-power semiconductor laser with nearly diffraction limited narrowband emission was designed and fabricated. The monolithic master oscillator power-amplifier (MOPA) diode laser consists of distributed Bragg gratings, a narrow ridge waveguide and a tapered amplifier. The ridge waveguide with length of 8 mm and width of 3 μm is used as the single-mode seed source. A tapered gain section with length of 7 mm and a full taper angle of 3.3° amplify the seed power. The fabricated device reach an output power of 10.3 W with a slow axis beam quality M² (1/e²) factor of 1.06 and an electro-optic efficiency of 50.5% . The spectral linewidth is 40 pm (3 dB), and a central wavelength tuning range of 4 nm was realized by the integrated Bragg gratings micro heater.