A gas sensor comprising: a sensor element that senses the concentration of a specific component in a measurement gas; a housing that has the sensor element inserted therein; and an element cover arranged on a distal side of the housing, wherein the element cover includes an inner cover arranged so as to cover a distal end portion of the sensor element and an outer cover arranged outside the inner cover, the outer cover has an outer introduction hole for introducing the measurement gas and an outer discharge hole formed on the distal side of the outer introduction hole, the inner cover has an inner introduction hole for introducing the measurement gas, which is formed on a proximal side of the outer introduction hole, and an inner discharge hole formed on the distal side of the inner introduction hole, in the inner cover, there is formed a reduced-diameter shoulder portion whose diameters are reduced distalward, the reduced-diameter shoulder portion is axially positioned between the outer introduction hole and the inner introduction hole, and the following relationship is satisfied: A/B ≤ 2.1, where A is an inner diameter of the inner cover and B is a maximum radial length of the distal end portion of the sensor element, wherein at least part of the reduced-diameter shoulder portion of the inner cover is provided proximalward from a position which is axially distant from a distal end of the sensor element by C, where C is a maximum radial distance between the distal end portion of the sensor element and the inner cover characterized in that a tubular protective cover, which is open on the distal side, is arranged radially outside the outer cover so as to completely cover the outer introduction hole, between the outer cover and the protective cover, there is formed a predetermined interspace, and a blackening process is performed on the inner surface of the inner cover. a sensor element that senses the concentration of a specific component in a measurement gas; a housing that has the sensor element inserted therein; and an element cover arranged on a distal side of the housing, wherein the element cover includes an inner cover arranged so as to cover a distal end portion of the sensor element and an outer cover arranged outside the inner cover, the outer cover has an outer introduction hole for introducing the measurement gas and an outer discharge hole formed on the distal side of the outer introduction hole, the inner cover has an inner introduction hole for introducing the measurement gas, which is formed on a proximal side of the outer introduction hole, and an inner discharge hole formed on the distal side of the inner introduction hole, in the inner cover, there is formed a reduced-diameter shoulder portion whose diameters are reduced distalward, the reduced-diameter shoulder portion is axially positioned between the outer introduction hole and the inner introduction hole, and the following relationship is satisfied: A/B ≤ 2.1, where A is an inner diameter of the inner cover and B is a maximum radial length of the distal end portion of the sensor element, wherein at least part of the reduced-diameter shoulder portion of the inner cover is provided proximalward from a position which is axially distant from a distal end of the sensor element by C, where C is a maximum radial distance between the distal end portion of the sensor element and the inner cover characterized in that a tubular protective cover, which is open on the distal side, is arranged radially outside the outer cover so as to completely cover the outer introduction hole, between the outer cover and the protective cover, there is formed a predetermined interspace, and a blackening process is performed on the inner surface of the inner cover.