Herein, a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAAm) was grafted on a Ta₂O₅ gate surface by surface-initiated atom transfer radical polymerization. We found that the phase transition behaviour from swelling state to deswelling state in response to temperature change was electrically detected in real time by using the PNIPAAm-grafted gate FET.