A bulk acoustic wave resonator may include: an air cavity; an etching stop layer and an etching stop part, which define a lower boundary surface and a side boundary surface of the air cavity; and a resonating part formed on an approximately planar surface, which is formed by a upper boundary surface of the air cavity and a top surface of the etching stop part. A width of a top surface of the etching stop part may be greater than a width of a bottom surface of the etching stop part. A side surface of the etching stop part connecting the top surface of the etching stop part to the bottom surface of the etching stop part may be inclined.