PURPOSE: To obtain a thin film piezoelectric oscillator by epitaxially growing an oxide single-crystal thin film and a silicon single-crystal thin film on a silicon substrate, deleting by etching a part of the substrate to form a diaphragm and forming an electrode, etc. on the diaphragm.

CONSTITUTION: An oxide single-crystal thin film 32 and then a silicon single- crystal thin film 33 are epitaxially grown on a silicon substrate 31. Then an etching protection film 34 is formed on both sides of the substrate 31 and then deleted at an area where a diaphragm is formed to give etching to the substrate 31. Then the films 34 and 32 are removed with a proper etching solution to obtain a silicon diaphragm with its fringe part supported by the substrate 31. Furthermore a foundation electrode 35, a piezoelectric thin film 36 and an upper electrode 37 are formed successively to obtain a thin film piezoelectric oscillator.