Abstract-We propose the design of a novel and highly efficient all-dielectric, three-waveguide polarization splitter based on the phenomenon of resonant tunneling. By considering a glass waveguide structure with an intermediate high-index guiding layer (such as silicon), we show that one can obtain extinction ratios better than -30 dB in both the outer waveguides at a particular thickness of the high-index layer. We have also estimated the tolerance required with respect to the separation between the middle and outside guides and the thickness of the high-index layer of such a device. The proposed design should be of interest in the realization of in-line fiber-optic polarization splitters and in integrated optics.