GaInAs/AlGaAs comprehensive-strained three-quantum-well lasers with asymmetric waveguide are designed and optimized. With this design, the optical field in the transverse direction is extended, and a semiconductor laser with large spot is obtained. For a 300-\mu m cavity length and 100-\mu m aperture device under continuous wave (CW) operation, the measured vertical and horizontal far-field divergence angles are 12.2o and 3.0o, respectively. The slope efficiency is 0.44 W/A and the lasing wavelength is 917 nm. The equivalent transverse spot size is 3 \mu m for the fundamental transverse mode, which is a sufficiently large value for the purpose of coupling and manipulation of light.