A split gated silicon nanotube field-effect transistor (FET) biosensor has been proposed for the label free detection of the biomolecules for the first time in literature. The sensitivity of the sensing device has been analysed considering the on current (ION) and the threshold voltage (Vth) variation. Sub-threshold regime has been considered here to detect the charged/neutral biomolecules. Extensive simulations have been done using the SILVACO ATLAS. Sensitivity analysis has been carried out by considering half-filled and full-filled nanogaps with the neutral or charged biomolecules inside the cavity. Significant sensitivity and excellent reduction in short-channel effects has been observed in proposed biosensor.