This manuscript presents the analytical model of a novel biosensor called Graded JAM Split Gate-All-Around (GJAM-SGAA) Bio-FET for the detection of Avian Influenza antibody and DNA. The GJAM-SGAA Bio-FET utilizes a silicon Gate-All-Around FET which operates in the Junctionless Accumulation Mode (JAM), with a graded doping in the channel. This Bio-FET also features a gate underlap double sided cavity that enables detection of biomolecules without the use of labels. Gate underlap cavities overcome the fabrication complexity of nanocavities and provides structural stability. A comparative analysis between the GJAM-SGAA Bio-FET and non-graded JAM Split Gate-All-Around FET (SGAA-FET) demonstrates that the proposed BioFET has 5.72 times higher ION current sensitivity, 5.3 times increase in threshold voltage sensitivity (SVth), and 2.13 × 102 times improvement in switching ratio sensitivity for avian influenza biomolecule. The SVth of proposed biosensor is compared with the existing biosensors and found that a triple-metal engineered gate and graded doped channel substantially boosts the sensitivity of proposed biosensor.