We present a three-dimensional (3D) particle focusing channel using the positive dielectrophoresis (pDEP) guided by a dielectric structure between two planar electrodes. The dielectric structure between two planar electrodes induces the maximum electric field at the center of the microchannel and particles are focused to the center of the microchannel by pDEP as they flow from the single sample injection port. Compared to the previous 3D particle focusing methods using standing surface acoustic wave (SSAW), hydrodynamic force, and negative dielectrophoresis (nDEP), the present device achieves the simple and effective particle focusing function without any additional fluidic ports and top electrodes. The present focusing channel is also fabricated by PDMS and glass substrate with electrodes, compatible for the integrated microbiochemical analysis system. We designed and fabricated the particle focusing channel based on the numerical estimation of particle position and focusing efficiency. In the experimental study, approximately 90% focusing efficiency was achieved within the focusing length of 2 mm, on both the x-z plane (top-view) and y-z plane (side-view) for 2 microm-diameter polystyrene (PS) beads at the applied voltage over 15 V(p-p) (square wave) and at a flow rate below 0.01 microl/min. Focusing experiments using 4.5 microm-diameter PS beads and yeast cells also verified that the present focusing channel can be applied to bio-particles having different sizes and properties. The present simple 3D particle focusing channel is suitable for use in integrated microbiochemical analysis systems.