Herein, we performed a computational investigation of a unique scheme of an exceedingly responsive plasmonic sensor comprises of a half-ring air cavity. By employing the finite element method, the spectral features and electric field distribution are determined. A sensitivity (S) of 600 nm/RIU was obtained by the standard sensor configuration, which is additionally enriched by employing nanodefects (NDs) in the air cavity. The NDs integrated half-ring cavity configuration can provide S and figure of merit (FOM) of 1084.21 nm/RIU and 57.06, respectively.