A method for making a crystal oscillator , characterized by the steps of: a) forming a first electrode portion on a surface of a piezoelectric substrate , so as to obtain a first semi-finished product ; b) attaching the first semi-finished product on a temporary substrate with the first electrode portion facing the temporary substrate ; c) thinning the piezoelectric substrate of the first semi-finished product , so as to obtain a thinned piezoelectric substrate having a first thickness (T1) and having a first surface on which the first electrode portion is formed; d) forming a second electrode on a second surface of the thinned piezoelectric substrate opposite to the temporary substrate , the second electrode including a second electrode portion having at least one opening , and a second extending electrode portion extending outwardly from the second electrode portion and disposed on a peripheral region of the thinned piezoelectric substrate , a projection of the second electrode portion on the second surface of the thinned piezoelectric substrate partially overlapping a projection of the first electrode portion on the second surface of the thinned piezoelectric substrate ; e) forming a first extending electrode portion that extends from the first electrode portion along a side surface of the thinned piezoelectric substrate to the second surface of the thinned piezoelectric substrate ; f) forming a hollow frame on the second surface of the thinned piezoelectric substrate , the hollow frame surrounding the second electrode portion , and disposed on the second extending electrode portion ; and g) etching a portion of the thinned piezoelectric substrate in positional correspondence with the at least one opening using the second electrode as a mask. a) forming a first electrode portion on a surface of a piezoelectric substrate , so as to obtain a first semi-finished product ; b) attaching the first semi-finished product on a temporary substrate with the first electrode portion facing the temporary substrate ; c) thinning the piezoelectric substrate of the first semi-finished product , so as to obtain a thinned piezoelectric substrate having a first thickness (T1) and having a first surface on which the first electrode portion is formed; d) forming a second electrode on a second surface of the thinned piezoelectric substrate opposite to the temporary substrate , the second electrode including a second electrode portion having at least one opening , and a second extending electrode portion extending outwardly from the second electrode portion and disposed on a peripheral region of the thinned piezoelectric substrate , a projection of the second electrode portion on the second surface of the thinned piezoelectric substrate partially overlapping a projection of the first electrode portion on the second surface of the thinned piezoelectric substrate ; e) forming a first extending electrode portion that extends from the first electrode portion along a side surface of the thinned piezoelectric substrate to the second surface of the thinned piezoelectric substrate ; f) forming a hollow frame on the second surface of the thinned piezoelectric substrate , the hollow frame surrounding the second electrode portion , and disposed on the second extending electrode portion ; and g) etching a portion of the thinned piezoelectric substrate in positional correspondence with the at least one opening using the second electrode as a mask. <EOS>