According to one embodiment, a gas sensor is disclosed. The gas sensor includes a substrate region, a first electrode provided on the substrate region, and a movable structure above the first electrode. The movable structure includes a deformable member which deforms by absorbing or adsorbing a predetermined gas, a heat member which heats the deformable member, and a second electrode. The gas sensor further includes a first cavity region which is provided between the first electrode and the second electrode.