In this paper, the image sensor using the a-Si:H TFT is proposed. The optimum amorphous silicon thin film is deposited using plasma enhanced chemical vapor deposition (PECVD). TFT and photodiode both with the thin film are fabricated and form image sensor. The photodiode shows that $I_{dark};is;{sim}10^{-13};A,;I_{photo};is;{sim}10^{-9};A;and;I_{photo}/I_{dark};is;{sim}10^4$, respectively. In the case of a-Si:H TFT, it indicates that $I_{on}/I_{off};is;10^6$, the drain current is a few ${mu}A;and;V_{th};is;2{sim}4$ volts. For the analysis on the fabricated image sensor, the reverse bias of -5 volts in ITO of photodiode and $70 {mu}sec$ pulse in the gate of TFT are applied. The image sensor with good property was conformed through the measured photo/dark current.