Abstract: A mass flow sensor includes a semiconductor substrate 1, an insulating thin film 2, heaters 311 and 312, temperature measurement resistors 321 and 322, and a protective layer 4. The heaters 311 and 312 are formed on the surface of the insulating thin film 2, and are provided adjacently such that the heater 311 is provided upstream the heater 312 and the heater 312 is provided downstream the heater 311. A cavity 5 is formed below the heaters 311 and 312, and the heaters are thermally insulated from the remaining portion of the semiconductor substrate. The temperature measurement resistors 321 and 322 are formed on the top surface of the insulating thin film 2, and are provided at opposite sides of the heaters 311 and 312, such that the resistors are aligned with respect to the flow passage of a fluid. In the mass flow sensor and the mass flowmeter including the sensor, the flow rate and flow direction of a fluid can be detected by means of merely the heaters 311 and 312, which are active elements.