In this paper, a Z‐shaped gate dielectric modulated (DM) tunnel field‐effect transistor‐(TFET) based biosensor with extended horizontal n+ pocket in the source region is proposed and different performances were investigated. Effective structural modification has been done by considering the filed induced quantum confinements effects to enhance the various performances of the device in terms of ON current (I_on) and threshold voltage. The horizontal pocket beneath the source region of the ZHP‐DM‐TFET biosensor enables the vertical tunneling besides the lateral tunneling which leads to enhancement of device performance in terms of short channel effects, low OFF the current. A comparative study is also carried with existing biosensors and it is observed that the ZHP‐DM‐TFET biosensor shows superiority over the other biosensors due to its irregular arrangement of the gate and the horizontal n+ pocket provides. The sensitivity analysis of the device was further investigated by varying the dielectric constant of the biomolecules inside the nanocavity for the value from K = 1 to K = 10. The ZHP‐DM‐TFET biosensor shows a significant improvement in threshold voltage sensitivity 20% (k = 2), 35%(K = 4) and a 10² improvement in I_on/I_off ratio. The impact of the thickness of the n+ pocket (pocket) over the sensitivity of the biosensor is also investigated.