A dynamic quantity sensor includes a sensor chip having a movable portion at one surface side thereof and a silicon layer at another surface side thereof. The movable portion is displaced under application of a dynamic quantity. The silicon layer is separated from the movable portion through an insulator. The dynamic quantity sensor also includes a circuit chip for transmitting/receiving electrical signals to/from the sensor chip. The circuit chip is disposed to confront the one surface of the sensor chip through a gap portion and cover the movable portion. The sensor chip and the circuit chip are bonded to each other around the gap portion so that a bonding portion is formed to substantially surround the gap portion and thereby seal the gap portion.