Technology capable of suppressing performance variation for each flow sensor and enhancing the performance is provided. According to a flow sensor of an embodiment, a local cavity CAV is provided on an upper surface SUR (MR) of a resin MR to generate an eddying current in a counterclockwise direction, so that an advancing direction of gas (air) that collided to an exposed side surface of a semiconductor chip CHP1 can be changed to an eddying direction instead of a direction toward an upper side of the semiconductor chip CHP1 differing by 90 degrees. Therefore, according to the flow sensor of the embodiment, the flow of the gas (air) at an upper side of the flow sensing unit FDU can be stably made smooth without being disturbed, whereby a flow sensing accuracy in the flow sensing unit FDU can be enhanced.