The present invention relates to a gas sensor and a manufacturing method thereof. A sensor body of the gas sensor is formed by cutting a multi-layered ceramic/metal platform where a plurality of sequential layer structures of a ceramic dielectric material and metal are layered in a layering direction. The sensor body includes at least one layered body wherein a ceramic dielectric material, a first internal electrode, a ceramic dielectric material, and a second internal electrode are sequentially layered. The first internal electrode and the second internal electrode are exposed through a cut surface by cutting. The first internal electrode is electrically connected to a first electrode terminal disposed on a first side of the sensor body, and the second internal electrode is electrically connected to a second electrode terminal disposed on a second side of the sensor body facing the first side. The first and the second internal electrode are exposed to form a sensing surface on at least one side of the sensor body excluding a side where the first and the second electrode terminal are installed. A gas sensing material layer for gas detection is formed on a portion or an entire upper portion of the sensing surface, or a metal film whose contact resistance with the gas sensing material layer is lower than the first and the second internal electrode is formed on upper portions of the first and the second internal electrode which are exposed and a gas sensing material layer for gas detection is formed on a portion or an entire upper portion of the sensing surface where the metal film is formed.