We report on a new type of high-power, single-mode vertical-cavity surface-emitting laser (VCSEL) based on the lasing of a slow-light mode laterally propagating in a long-apertured VCSEL structure. A VCSEL length of 500 μm produces high single-mode power with narrow beam divergence for sensing and 3D imaging applications. Slow-light modes show a lower threshold current and better beam quality. We found the optical resonance in the oxidized region at the end of a mesa helps when selecting a transverse mode. We obtained a quasi-single-mode power of 22 mW under continuous-wave operation. This result shows the possibility to achieve high single-mode power and high beam quality by introducing a mode selection mechanism.