Achieving nanoconfinement-controlled synthesis of nanoplatelets (NPLs) via solution process under ambient condition remains a challenge. In this work, we developed a general ligand-induced strategy to synthesize colloidal stable all-inorganic semiconductor NPLs with controllable lateral dimensions. By introducing certain metal salts (cations: Zn²⁺ and In³⁺, anions: NO₃⁻, BF₄⁻, or triflate OTf⁻), wurtzite-structured (WZ-) CdS, CdSe, CdTe, and alloy Cd_1−xZn_xSe NPLs were directly synthesized in solution through the controlled diffusion of magic-size clusters (MSCs) at room temperature. Mechanism studies revealed that destabilization of MSCs and nanoconfined growth in templates facilitated the formation of NPLs. The present study not only provides a new synthetic route for the preparation of NPLs but also helps to provide insight into their probable formation mechanism and presents an important advance toward the rational design of functional nanomaterials.