This study presents a comprehensive model for characterizing biomolecule species using one naturally off AlGaN/GaN MOSHEMT tailored for biosensor applications. With the increasing demand for biosensors in various fields such as drug discovery, medical diagnosis, and environmental monitoring, there is a growing need for high sensitivity and low limits of detection. Bio-FETs offer promise as label-free sensors for rapid detection of bacteria and proteins. Leveraging the unique properties of AlGaN/GaN HEMTs, this study investigates their suitability for biosensing applications, particularly when an AlGaN barrier layer is formed atop GaN, facilitating biomolecule bonding to its surface. The proposed analytical model of the AlGaN/GaN MOSHEMT incorporates modulation of dielectric for electrical detection in a label free manner, allowing for the characterization of biomolecule occupancy. By utilizing the Poisson equation and dielectric modulation, operative capacitance in the crater area and the VTh are determined. Variations in threshold voltage and drain current serve as sensing metrics for detecting biomolecules within the cavity region. Notably, the molar fraction of aluminium in the AlGaN layer significantly influences the dielectric constant, thereby impacting sensitivity. Through modelling the sensing behaviour of the MOSHEMT with varying molar fractions in the barrier AlGaN layer, this study provides insights into optimizing biosensing performance.