A crystal oscillator includes an oscillating substrate, a hollow frame, a first electrode, and a second electrode. The oscillating substrate includes a main oscillating region and a thinned region that has a thickness smaller than that of the main oscillating region. The first and second electrodes are disposed on a first surface of the oscillating substrate and a second surface opposite to the first surface, respectively. The hollow frame is disposed on the second surface. The second electrode includes a second electrode portion that has at least one opening in positional correspondence with the thinned region. A method for making the crystal oscillator is also provided herein.