Provided is a gas sensor which achieves a reduction in the power consumption of a heater and downsizing by configuring a pump cell (3) and a sensor cell (5) from one solid electrolyte body (2), a pump electrode (30), a sensor electrode (50), and a reference electrode (80). By making the ratio of the shortest distance (L2) between the pump electrode (30) and the sensor electrode (50) to the thickness (d) of the solid electrolyte body (2) 3 or more, in a gas sensor (1), the pump cell (3) and the sensor cell (5) can be configured from one solid electrolyte body (2), the pump electrode (30), the sensor electrode (50), and the reference electrode (80). Therefore, only either a gas chamber or a reference chamber is present between the solid electrolyte body and the heater, thereby the distances between the pump cell and the heater and between the sensor cell and the heater can be reduced, and the pump cell and the sensor cell can be easily heated by the heater.