In this work, the design and performance analysis of a dielectric modulated N+ P+ I N+ P+ feedback field-effect transistor (FBFET) based label-free bio-sensor have been presented in detail. The extremely steep switching characteristics of FBFET enable the proposed biosensor to detect bio-molecules at higher sensitivity through positive feedback mechanism. We have introduced an intrinsic region of low-bandgap SiGe material between two channels of the device and created a cavity above this region to study biosensor performance. Sensitivity analysis has been performed on biomolecules with a wide permittivity (K) ranging from 1 to 22. The highest ON-drive current (ION), ON–OFF current ratio (ION/OFF), ON current sensitivity (SION), ON–OFF current sensitivity (SION/IOFF), best subthreshold swing parameter and the lowest threshold voltage (VTh) have been achieved as 7.7×10−5 A/μm, 2.81×1011, 5.87×102, 4.48×102, 0.036 mV/decade and 0.212 V respectively. In this study, the influence of biomolecule permittivity, positively and negatively charged biomolecules, cavity length and thickness, nano-cavity filling profile and filling factor, temperature, as well as the interface trap charge density on the performance metrics of the proposed device including ION, ION/OFF ratio, SION, SION/IOFF, and VTh have been analyzed in this study. The Sentaurus TCAD tool has been utilized to design the device and analyze its electrical characteristics.