A package is configured such that a length in a direction parallel to a semiconductor chip is larger than a length in a direction orthogonal to the semiconductor chip, and the package includes a substrate to which the semiconductor chip is electrically connected and fixed, a side wall firmly attached to the substrate, and a cover firmly attached to the side wall. The package includes a detection space in which gas flows around the semiconductor chip. The package includes openings formed in the side wall and/or between the side wall and the cover and communicated with the detection space.