Electro cell fusion has significant potential as a biotechnology tool with applications ranging from antibody production to cellular reprogramming. However due to low fusion efficiency of the conventional electro fusion methodology the true potential of the technique has not been reached. In this paper, we report a new method which takes cell fusion efficiency two orders magnitude higher than the conventional electro fusion method. The new method, based on one-to-one pairing, fusion and selection of fused cells was developed using a microfabricated device. The device was composed of two microfluidic channels, a micro slit array and a petri dish integrated with electrodes. The electrodes positioned in each channel were used to generate electric field lines concentrating in the micro slits. Cells were introduced into channels and brought in to contact through the micro slit array using dielectrophoresis. The cells in contact were fused by applying a DC pulse to electrodes. As the electric field lines were concentrated at the micro slits the membrane potential was induced only at the vicinity of the micro slits, namely only at the cell-cell contact point. This mechanism assured the minimum damage to cells in the fusion as well as the ability to control the strength and location of induced membrane potential. We introduced mouse embryonic stem cells and mouse embryonic fibroblasts to the microfluidic channels and demonstrated high-yield fusion (> 80%). Post-fusion study showed the method can generate viable hybrids of stem cells and embryonic fibroblasts. Multinucleated hybrid cells adhering on the chip surface were routinely obtained by using this method and on-chip culturing.