In music, a 128th note in American English, or a semihemidemisemiquaver or quasihemidemisemiquaver in British English, is a note that is half as long as a sixty-fourth note. It has a total of five flags or beams.

Notes this short are very rare in printed music, but not unknown. They are principally used for brief, rapid sections in slow movements. For example, they occur in the first movement of Beethoven's Sonata "Pathetique" Op. 13, to notate rapid scales.

These five-beamed notes also appear occasionally where a passage is to be performed rapidly, but where the actual tempo is at the discretion of the performer rather than being a strict division of the beat. In such cases, the aggregate time of the notes may not add up exactly to a full measure, and the phrase may be marked with an odd time division to indicate this. Sometimes such notation is made using smaller notes, sized like grace notes.