A method of manufacturing a display device is provided. A method of manufacturing a display device comprises preparing a thin film forming apparatus including a crucible, which stores a source material for forming a thin film, and a front heatsink, which is disposed on the crucible and includes a reflective plate, wherein the reflective plate has a first surface with a first reflectivity and a second surface with a second reflectivity, which is different from the first reflectivity; and forming a thin film on a substrate by evaporating the source material of the thin film forming apparatus.