The invention relates to a piezoelectric resonator, which comprises a base and at least two vibrating arms (3) extending from the base, at least two grooves (4a, 4b) being formed opposite each other on part of the length of the arms and on upper and lower faces of the arms. The depth of the groove on the upper face is less than 30% of the total thickness of each arm and the depth of the groove on the lower face is more than 50% of the total thickness of each arm, or reversely.