A gas sensor includes a ceramic wiring board having an opening and a sensor element fixedly suspended within the opening through electricity conducting members. A distal end portion of the ceramic wiring board is accommodated in a casing, and a proximal end portion extends to the outside of the casing. Electrically conductive pads connected to the electricity conducting members through lead traces are disposed on the front and back surfaces of the proximal end portion. The width of the distal end portion is larger than the width of a narrow region of the proximal end portion that includes the electrically conductive pads and portions of the lead traces. The gas sensor further includes a tubular insulator circumferentially surrounding the narrow region and a plurality of spring terminals that are accommodated in the insulator and come into elastic contact with the electrically conductive pads.