Using dielectric modulated biosensors, labelfree biosensing could be obtained by appropriate tuning the dielectric constants (K) of the cavity region, which is mimicked as the presence/absence of the biomolecules. In this paper, a compound semiconductor GaAs 1-x Sb x based FinFET, has been investigated as a dielectric modulated (DM) label-free biosensor. By employing well-calibrated TCAD models, the sensitivity metrics of the proposed biosensor have been explored for dry and watery environments. In addition, the reaction time of the biosensor under the presence of biomolecules has been analyzed using transit time/frequency calculations. Test biomolecules such as Biotin (K$\approx$2.63) and Gelatin (K$\approx$12) have been taken into consideration for the proposed study. Further, to mitigate the impact of the hot carrier effect in the sensing, a lightly doped drain (LDD) architecture is employed and investigated to enable the high Geld operation.