This article models a dielectrophoresis based approach for achieving 3D focusing, of micro-scale objects, in microfluidic devices. The microfluidic device employs four planar electrodes; two electrodes each on the top and bottom surface of the microchannel and each slightly protrude into the microchannel. Each electrode establishes electric field with the neighboring electrode on the same and opposite surfaces. The dielectrophoretic force pushes the micro-scale objects both the directions transverse to the flow direction to achieve the desired 3D focusing. The developed model accounts for various forces such as that associated with inertia, sedimentation, drag, and dielectrophoresis. Finite difference method is used for calculating the electric field and dielectrophoretic force as well as the displacements of micro-scale objects in the microchannel. Several geometric and operating parameters influence the trajectory of micro-scale objects. There exists a threshold voltage beyond which there is no increase in levitation height.