A method of manufacturing an accelerometer sensor having a mass portion is disclosed. A P-type silicon area is formed in an upper area of a P-type silicon substrate by means of impurity doping. An N-type silicon layer is formed on the silicon substrate through vapor phase epitaxy. A recess defining the mass portion is formed in the silicon substrate through an etching process. A current is supplied to the silicon substrate in an electrolytic solution, such as HF aq., while the substrate is connected to an anode of a power supply. The P-type silicon area is then converted to a porous silicon area. The porous silicon area is subjected to a wet etching to be hollowed, thus obtaining a mass portion of a desired shape.