A chip on film package is disclosed, including a flexible film and a chip. The flexible film includes a film base, a patterned metal layer includes a plurality of pads and disposed on an upper surface of the film base, and a dummy metal layer covering a lower surface of the film base and capable of dissipating heat of the chip. The dummy metal layer comprises at least one opening exposing the second surface, and at least one of the plurality of pads is located within the at least one opening in a bottom view of the chip on film package. The chip is mounted on the plurality of pads of the patterned metal layer.