To provide a method of manufacturing a MEMS (Micro Electro Mechanical Systems) device capable of preventing the structure of the MEMS device from being destroyed when a SOI (Silicon On Insulator) wafer is separated into each of the MEMS devices and preventing falling of the MEMS devices after the separation.

A surface groove 21 of a depth getting to an embedded oxide film 10b is formed by etching in a region corresponding to a street of the SOI wafer 10 in a silicone layer 10c. A rear face groove 22 of a depth getting to the embedded oxide film 10b is formed by etching in a region corresponding to the street in a supporting substrate 10a. The embedded oxide film 10b is separated into each of the MEMS devices 1 by being etched by etching gas. The rear face groove 22 is formed to individually surround each device region corresponding to each of the MEMS devices 1. The surface groove 21 is formed to be provided with an extension part 17 extended from the device region in the silicone layer 10c.