Producing high performance phosphors using abundant and non‐toxic precursors yet straightforward methods are promising but still a challenging task. Herein, highly luminescent and thermally stable phosphors were fabricated through an in situ precipitation synthesis strategy. Sulfur nanodots (S‐dots) act as the precursors for precipitation reactions and also provide the luminescent centers. Structural and optical characterization investigations suggest that S‐dots are incorporated in the matrix of BaSO4, and BaSO4 provides passivation effect for the surface ligands or traps of S‐dots. This results in the promotion of photoluminescence quantum yield from 23 % to 58 %, and the BaSO4 matrix also leads to the obvious promotion of thermal stability. These merits endow the construction of phosphor‐based light‐emitting diodes by utilizing the S‐dots@BaSO4 hybrid phosphors as a color conversion layer. These research results are significant for developing sulfur‐based luminescent materials, and also provide a solid and universal theory to produce high quality phosphors. [ABSTRACT FROM AUTHOR]