In a sensor chip for a fluid flow sensor, a thin film portion is formed above a hollow cavity portion while leaving thin film layers formed on the surface of a substrate. A conductor is provided on the inner wall face of a through hole formed to penetrate the substrate to thereby electrically connect a detecting portion constituted by a conductor film in the thin film layers and a substrate conductor portion formed on the rear face side of the through hole. The surface of a circuit board is formed with a control circuit and a base conductor portion electrically connected to the control circuit. The sensor chip and the circuit board are layered and the substrate conductor portion and the base conductor portion are electrically connected.