▎ 摘　　要

NOVELTY - The gas sensor (100) has semiconductor layer (101-103). The graphene film (105) is provided in upper direction of semiconductor layer, and contacts gas. The barrier film (104) is positioned between the semiconductor layer and the graphene film. The two electrodes are provided in the surface of the semiconductor layer and positioned the downward portion of the barrier film. An interlayer insulation film covers the barrier film. The graphene film is provided on interlayer insulation film, and electrically contacts with barrier film through conductive layer in insulation film. USE - Gas sensor used for medical device and diagnostic apparatus for detecting chemical substance contained in gas such as ammonia, and for detecting ammonia of ppb level in diagnosis of stomach cancer. ADVANTAGE - The detection sensitivity of gas is improved, by the appropriate graphene film, barrier film, and a semiconductor layer. The power-saving is achieved, since measuring is achieved without sending drain current. The cost reduction and size reduction is achieved. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for an usage method of the gas sensor. DESCRIPTION OF DRAWING(S) - The drawing shows the sectional view of the structure of the gas sensor. Gas sensor (100) Semiconductor layers (101-103) Barrier film (104) Graphene film (105) Gate electrode (106)