A novel cladding structure is proposed and analyzed for semiconductor quantum-well lasers to achieve a small vertical-beam divergence and a low threshold current density simultaneously. This cladding structure is designed to guide a wide optical mode but with a high peak intensity in quantum wells. The wide expansion of the optical mode results in a small beam divergence. In addition, the high optical intensity in quantum wells causes a low threshold current density. This novel cladding structure is optimized. The result shows that this type of cladding structures can achieve a beam divergence as small as 14.6° while the threshold current density remains small.