A compact polarization demultiplexer (P-DEMUX) composed of a microring resonator in strip waveguides and two bus channels in slot waveguides is proposed and characterized. The modal indices of the TM modes for slot and strip waveguides have comparable values, while those for the TE modes show large differences. With these unique properties, the input TE mode can directly output from the through port with nearly neglected coupling, while the input TM mode can efficiently output from the drop port at the resonant wavelength. Results show that a P-DEMUX with a radius of 3.069 μm is achieved, where the extinction ratios are ∼29.85 and 24.23 dB, respectively, for TE and TM modes, and the insertion losses are ∼0.45 and 0.26 dB, respectively, at the wavelength of 1550 nm. Moreover, fabrication tolerances to the structural parameters are investigated and field evolution along the propagation distance through the P-DEMUX is demonstrated.