A method of manufacturing a semiconductor device includes: coupling a semiconductor die to a protection layer; forming a first redistribution layer over the semiconductor die, wherein the first redistribution layer includes a first conductive plate of an antenna structure and a first dielectric layer laterally surrounding the first conductive plate; etching the first dielectric layer to form a recess exposing the first conductive plate; filling the recess with a second dielectric material to form an insulating film; and forming a second redistribution layer including a second conductive plate of the antenna structure over the insulating film. The insulating film electrically isolates the first conductive plate from the second conductive plate, wherein one of the first conductive plate and the second conductive plate is configured to radiate or receive electromagnetic wave. The insulating film has a thickness associated with a main resonance frequency of the antenna structure.