Abstract: The present invention relates to a film bulk acoustic wave device and a method of manufacturing the same, wherein comprising an acoustic reflective layer which is formed on a substrate by removing a sacrificial layer on the substrate and becomes an empty space; an oxidation protective film or etch protecting film which is formed in a pattern that divides a resonance region to form the acoustic reflective layer on the sacrificial layer; a thermal oxidation film which is formed by partially thermally oxidizing the sacrificial layer in an electrode region where the oxidation protective film or the etch protecting film is not formed; and a lower electrode, a piezoelectric thin film, and an upper electrode all of which are disposed on the thermal oxide. Further, the present invention is directed to a method of manufacturing the same.