Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top.
F#m7b5 is F#, A, C and E — F#m7 with the fifth lowered a semitone.
It sounds hollow, and unmistakably going somewhere. Almost always the first chord of a minor ii–V–i, so it walks straight into an altered dominant.

| F# | A | C | E |
|---|---|---|---|
| 1 | ♭3 | ♭5 | ♭7 |
Pre-dominant — the ii of a minor key.
Also written F#ø, F#ø7, F#m7-5, F#m7(b5) or F# half diminished. The same chord either way; which spelling you meet depends on who wrote the chart.
Root, third and seventh. The third and seventh, the guide tones, are what make the chord major, minor or dominant, so the fifth can go: it says nothing the symbol needs.
Three notes means a spare string, which is the real point. Put a tension on it.
F#m7b5 has 6 of them, on strings 6-4-3-2, the bottom four strings, strings 5-3-2-1 and the middle four strings, from open position up to the 13th — all in one inversion, so the bass note never moves. The one to learn first is the F# shape at the nut.
Start with x-9-10-9-10-x — no barre. 1 of the 8 shapes here sits in open position. 4 of the 8 need a barre. Together they cover the neck from the 1st fret to the 14th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| 202210 | open position | F#, root position | E | barred |
| 234252 | 2nd fret | F#, root position | F# | barred |
| xx4555 | 4th fret | F#, root position | A | barred |
| x97978 | 7th fret | F#, root position | C | all fretted |
| x-9-10-9-10-x | 9th fret | F#, root position | A | all fretted |
| x-x-10-11-10-12 | 10th fret | C, 2nd inversion | E | all fretted |
| 14-x-x-14-13-12 | 12th fret | F#, root position | E | all fretted |
| 14-x-14-14-13-x | 13th fret | F#, root position | C | barred |
The same notes rebuilt from scratch give 14 drop 2, 9 drop 3 and 6 open string voicings, each on its own page.
Tensions. A shell of F#m7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (B) and the b13 (D).
F#m7b5 is the ii of E minor, which is where it is nearly always found: half-diminished, then an altered dominant, then the minor tonic.
In which keys. Every note of F#m7b5 belongs to E minor (the ii°, the supertonic) and G major (the vii°, the leading tone).
Every note of F#m7b5 is in F# blues, F# locrian, F# altered and F# half-whole diminished.
Change one note of F#m7b5 and you have F#dim (drop the flat seventh), F#dim7 (the flat seventh becomes a sixth), F#m7 (the flat fifth becomes a fifth), F#mMaj7b5 (the flat seventh becomes a major seventh) or F#7b5 (the minor third becomes a major third).
F#m7b5 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On F#m7b5’s sound and use this page follows Mark Levine, The Jazz Theory Book (Sher Music, 1995). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.