This paper presents a unified analytical model to evaluate 2D-Electron Gas density in β -(AlxGa1−x)2O3/Ga2O3 δ-doped Heterostructure Field Effect Transistor. Further, the obtained unified model is then used to study the effect of spacer thickness, conduction band offset, and δ-doping density on the 2D-electron density. The study shows the efficacy of thin spacer layer in enhancing the 2D-electron density obtained at the β -(AlxGa1−x)2O3/Ga2O3 heterointerface. This observation is in-unison with the simulated results obtained using 1D Poisson-Schrodinger solver which could explain the behavior using conduction band energy diagrams. Similarly, high conduction band offset is conducive for higher 2D-electron density alongside eradicating parallel conduction. The current study also shows the effect of δ-doped layer in governing the onset of parallel conduction phenomenon. Thus, the presented comprehensive study will be essential for device designers to enhance the 2D-electron density at the heterointerface which is quintessential to achieve optimum drain current.