A gas sensor includes a sensor element having an electrode pad and a metal terminal member including a forward metal terminal member connected to the electrode pad, and a rear metal terminal member connected to the forward metal terminal member and a lead wire. The rear metal terminal member includes a forward end portion, a central portion, and a lead-wire connection portion. The forward end portion and the central portion are integrally connected through a first neck portion smaller in sectional area than the forward end portion and the central portion. The central portion and the lead-wire connection portion are integrally connected through a second neck portion smaller in sectional area than the central portion and the lead-wire connection portion. The first neck portion is greater in moment of inertia of area than the second neck portion.