In a method of forming a polysilicon film, a thin film transistor including a polysilicon film, and a method of manufacturing a thin film transistor including a polysilicon film, the thin film transistor includes a substrate, a first heat conduction film on the substrate, a second heat conduction film adjacent to the first heat conduction film, the second heat conduction film having a lower thermal conductivity than the first heat conduction film, a polysilicon film on the second heat conduction film and the first heat conduction film adjacent to the second heat conduction film, and a gate stack on the polysilicon film. The second heat conduction film may either be on the first heat conduction film or, alternatively, the first heat conduction film may be non-contiguous and the second heat conduction film may be interposed between portions of the non-contiguous first heat conduction film.