We developed a simple and general approach for constructing a wafer-scale monolayer, close-packed polystyrene (PS), and SiO2 sphere arrays, namely colloidal crystals, which have significant potential in various applications. The method combines slope self-assembly and thermal treatment to achieve large-area and high-quality colloidal crystal with a proper slant angle (θ) and latex concentration (volume fraction, φ). The dependence of the structures of colloidal crystals on a dispersion system was also investigated. Moreover, a theoretical analysis of the slope self-assembly method was proposed. In addition, we applied the method to assemble PS spheres on different kinds of substrates, which indicates that the method is a versatile and reliable way to fabricate monolayer colloidal crystals.