A gas sensor element includes a heating portion and a ceramic layer. The ceramic layer has a first and second face, and is configured to be heated by the heating portion. The ceramic layer has an open-hole portion extending therethrough in a thickness direction from the first face toward the second face and constituting a through-hole for electrically connecting the first face to the second face. The open-hole portion is demarcated by a first inner wall face, and a second inner wall defining a recessed portion that is recessed inward of the ceramic layer. With the ceramic layer having a thickness of 1, the length of the recessed portion to the most distal position thereof from a position on the first inner wall face that is closest to a center axis of the open-hole portion is 0.05 or more and 0.20 or less.