The present disclosure relates to a semiconductor package, which includes a carrier, a flip-chip die, a mold compound, and a heat spreader. Herein, the flip-chip die includes a device layer over the carrier and a die substrate over the device layer. The mold compound resides over the carrier and surrounds the flip-chip die. The mold compound has a recess adjacent to the flip-chip die, and the recess extends vertically lower than a top surface of the die substrate. The heat spreader hangs over the flip-chip die, and includes a spreader body that is thermally coupled to the die substrate, and a spreader protrusion that extends from the spreader body into the recess. A thickness of the spreader protrusion is shorter than a depth of the recess, and a width of the spreader protrusion is narrower than a width of the recess, such that the spreader protrusion is floating in the recess.