Based on separated asymmetric large optical cavity, the high power pulsed semiconductor lasers with epitaxially-stacked three-active-region structure at laser central wavelength of 905 nm are investigated. We optimize the critical parameters, including near-field optical intensity model, free-carrier absorption loss, the distance between adjacent luminescent regions and the doping levels of each layer, to obtain higher peak output power, lower internal optical loss and smaller far-field vertical divergence angle. A three-active-region high power semiconductor laser with 1 mm cavity length and 100 μm stripe width is developed. We achieve a peak output power of 122 W driven by 34.5 A pulse current intensity at 150 ns pulse width and 6.67 kHz repetition rate. Slope efficiency of 3.54 W/A, equivalent internal quantum efficiency of 91.75% and internal optical loss of 2.05 cm -1 for each emitter are obtained, and far-field divergence angles of 7.8° and 27.6° (full width at half maximum) are achieved in the lateral and vertical directions, respectively.