This paper reports a novel three degree of freedom (DoF) resonator whose mechanical system is the combination of a normal dual mass resonator (DMR) and an amplified dual mass resonator (ADMR). Stiffness perturbation between two outer masses causes mode coupling between DMR mode and ADMR modes which can be treated as anti-phase modes of DMR and ADMR, respectively. The amplitude ratio of two masses, which came from the mode localization, is highly sensitive to the stiffness perturbation. Mode localization in this novel design was validated both by the theoretical and the experimental studies. From the theoretical consideration, the sensitivity could be tuned by adjusting the stiffnesses. The measurement results showed the as-fabricated sensitivity was 209.6. The sensitivity could be enhanced to be 56679 by applying the DC bias of 39.3V to electrostatically soften the inner springs, which is consistent with the theoretical result.