The interface roughness and scaling exponent of strained-layer superlattices (SLSs) grown by molecular beam epitaxy (MBE) have been measured by x-ray reflectivity and diffuse-scattering methods. We have found that for samples grown under identical conditions the root mean square (rms) roughnesses , the roughness exponents (h), and the lateral correlation length are dependent upon the thickness and/or the substrate temperatures of the superlattice. The incorporation of a surfactant, such as antimony, can retard interface widening and smooth the interface.