A gas sensor (1) includes at least a sensor element (12) which measures the concentration of a specific gas component, a housing (13) which accommodates the sensor element (12), and a base portion (21) which is attached to the housing and is formed of resin. The base portion includes a first base portion (22) which is a portion of the base portion located on the side toward the housing and which is molded integrally with the housing, and a second base portion (23) which is molded separately from the first base portion, which is a portion of the base portion located opposite the housing, and which has a connector portion (23c) in which a plurality of terminals (26) electrically connected to the sensor element are disposed such that they extend in a direction intersecting the insertion direction of the sensor element.