The goal of this work is to analyze the effect of gate to drain underlapping on n-type Tunnel-FET (nTFET) devices, filled with different dielectric permittivity material (k) in order to simulate the bioelement materials. The results show that the use of Tunnel-FET ambipolar current presents high sensitivity for using it as biosensor devices for transistors with the drain underlap of 15 nm and total channel length of 50 nm for the range studied in this paper.