High wavelength shift coefficient varying with temperature and broad spectrum width are disadvantages of the output properties of high power broad-area semiconductor lasers. For improving the output spectral properties of broad-area semiconductor lasers, a volume-Bragg-grating (VBG) off-axis external cavity method was adopted with satisfied effect on spectrum and slope efficiency. The external cavity laser composes of a broad-area stripe semiconductor laser with fast-axis and slow axis beam collimation, and a VBG positioned off-axis. The broad-area stripe semiconductor laser has an emission width of 100 μm. High power output is achieved with 3.4 W at working current with 4.0 A. The slope efficiency is 1.0 W/A, and a narrower output spectrum of 0.2 nm width is realized compared with free output spectrum width of 2～3 nm. The wavelength shift coefficient varying with temperature is less than 0.015 nm/℃.