A method of manufacturing a semiconductor device includes: receiving a semiconductor structure having a chip region, a seal ring region surrounding the chip region, and a scribe region surroundingly defined around the seal ring region, the semiconductor structure including: a semiconductor chip in the chip region; and a molding compound disposed around the semiconductor chip and distributed in the chip region, the seal ring region and the scribe region; forming an insulating film over the chip region of the semiconductor structure and the seal ring region of the semiconductor structure; forming a seal ring over the seal ring region of the semiconductor structure and laterally adjacent to the insulating film, in which the seal ring has an exposed lateral surface facing away from the insulating film; and forming a protective layer that defines a substantially smooth and inclined lateral surface over the exposed lateral surface of the seal ring.