This work presents, for the first time, the design and performance evaluation of a dielectric-modulated N+ P P+ N+ P+ vertical feedback FET-based label-free biosensor, demonstrating its potential for highly sensitive biomolecule detection. This work takes advantage of the superior characteristics of the vertical structure over the planar design, combined with the ultra-steep switching enabled by the positive feedback mechanism of the FBFET, resulting in a substantial enhancement in biosensor performance. Although FBFETs offer significant promise as ultra-steep switching devices capable of enabling highly sensitive sensors, research in this domain is still in its nascent stage. This study provides a detailed analysis of performance variations and sensitivities arising from factors such as the permittivity of different biomolecules, the presence of charged biomolecules, nano-cavity thickness, cavity filling profiles, the percentage of biomolecule filling and interface trap charge density. The ON current (ION), ON-OFF current ratio (ION/IOFF), threshold voltage (VTh), and subthreshold swing parameter (SS) of the proposed biosensor are 2.8×10−4 A/μm, 6.57×1010, 0.442 V, and 1.6×10−3 mV/decade, respectively, for K (dielectric constant of the biomolecule) = 22. The proposed biosensor achieves maximum sensitivities of 2139, 395, 0.79, and 0.997 for ION, ION/IOFF, VTh, and SS, respectively. The combination of high sensitivities and ultra-low SS enables the device’s efficient use in future low-power biosensor applications.