This invention aims at providing a novel semiconductor accelerometer comprising a smaller number of substrates and a production method thereof.An insulating film is formed on a main plane of a P-type silicon substrate, and a beam-like movable electrode is formed on the insulating film. Fixed electrodes are then formed on both sides of the movable electrode in self-alignment with the movable electrode by diffusing an impurity into the P-type silicon substrate, and the insulating film below the movable electrode is etched and removed. There is thus produced a semiconductor accelerometer comprising the P-type silicon substrate 1, the movable electrode 4 having the beam structure and disposed above the P-type silicon substrate 1 with a predetermined gap between them, and the fixed electrodes 8, 9 consisting of the impurity diffusion layer and formed on both sides of the movable electrode 4 on the P-type silicon substrate 1 in self-alignment with the movable electrode 4. This sensor can detect acceleration from the change (increase/decrease) of a current between the fixed electrodes 8 and 9 resulting from the displacement of the movable electrode 4 due to acceleration.