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A novel microdevice for electrical impedance spectroscopy is presented to differentiate between normal and cancerous cells at the single cell level with a high sensitivity. The device utilizes a microfluidic tunnel structure, whose height is smaller than the cell diameters, to squeeze the target cells. Thus, the tight contact between the cells and electrodes allows the device to measure the intrinsic electrical properties of the cells with a higher sensitivity than through noncontact methods. Three-dimensional interdigitated electrodes (3-D IDE) are also employed to confine most of the electric field into the cell membrane, which contains the meaningful electrical properties. Consequently, the variance of the measured values could be reduced because the position of target cells is almost the same in every cell assay. The device well distinguishes normal human breast cells (MCF-10A) from early-stage human breast cancer cells (MCF-7) by means of electrical impedances at 500 kHz; the average differences of the real part and phase angle between the target cells are 44.4 and 1.41 , respectively. The proposed device also shows a high repeatability for the deionized (DI) water test conducted before and after each cell assay; the variances of the real part and phase angle of electrical impedance at 500 kHz are as small as 9.07 and 0.27 , respectively.