A bulk acoustic wave filter device and method thereof includes a first layer forming an air gap together with a substrate, a lower electrode disposed over the first layer, a piezoelectric layer disposed to cover a portion of the lower electrode, an upper electrode disposed over the piezoelectric layer, a frame layer disposed below the upper electrode, and a lower electrode reinforcing layer disposed on the lower electrode, other than portions in which the piezoelectric layer is disposed. The lower electrode reinforcing layer is formed by separating the lower electrode reinforcing layer from the upper electrode or the frame layer upon one of the upper electrode and the frame layer being formed.