A method of fabricating a vertically tapered structure. The method includes placing a spacer layer at a predetermined area on a wafer, placing a mask layer at a predetermined area on the spacer layer, and over-etching the spacer layer, by etching a certain area below the mask layer, fabricating a cantilever type shadow mask having the spacer layer and the mask layer. Thus, it is possible to fabricate the vertically tapered structure of several tens of microns. The vertically tapered structure can be used as the optical waveguide in the optical device to minimize junction loss that may occur between the optical waveguide and the optical fiber.