An energy-trap thickness extensional vibration mode piezoelectric resonator uses a harmonic of a thickness extensional vibration mode and effectively suppresses generation of unwanted spurious vibrations. The energy-trap thickness extensional vibration mode piezoelectric resonator includes a piezoelectric strip, first and second excitation electrodes located on opposite surfaces of the piezoelectric strip, and an internal electrode disposed inside the piezoelectric strip. The first and second excitation electrodes are located on opposite ends of the piezoelectric strip in an overlapping arrangement. The internal electrode is located opposite to the first and second excitation electrodes. The first and second excitation electrodes overlap each other over a length of l such that l/d is not greater than about 6, where d=t/n.