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.
C#mMaj7b5 is C#, E, G and B# — C#m7b5 with the seventh raised a semitone.
It sounds brittle and impossible to mistake. Scarce enough that most players meet it as a passing sonority rather than as a chord they chose.

| C# | E | G | B# |
|---|---|---|---|
| 1 | ♭3 | ♭5 | 7 |
Rare tonic — a half-diminished chord with its seventh raised instead.
Also written C#mM7b5 or C#m(maj7)b5. 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.
C#mMaj7b5 has 3 of them, on strings 5-3-2-1, strings 6-4-3-2 and the bottom four strings, from the 3rd fret up to the 8th — all in one inversion, so the bass note never moves. The one to learn first is the C# shape at the 3rd fret.
Start with x42010 — no barre and 2 open strings. 1 of the 6 shapes here sits in open position. 2 of the 6 need a barre. Together they cover the neck from the 1st fret to the 13th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x42010 | open position | C#, root position | E | 2 open strings |
| x4x553 | 3rd fret | C#, root position | G | all fretted |
| x4555x | 4th fret | C#, root position | E | barred |
| 9-10-x-9-8-8 | 8th fret | C#, root position | B# | all fretted |
| 9-10-10-9-x-9 | 9th fret | C#, root position | C# | barred |
| x-x-11-12-13-12 | 11th fret | C#, root position | E | all fretted |
The same notes rebuilt from scratch give 13 drop 2, 9 drop 3 and 3 open string voicings, each on its own page.
Tensions. A shell of C#mMaj7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (F#) and the b13 (A).
Every note of C#mMaj7b5 is in C# diminished.
Change one note of C#mMaj7b5 and you have C#dim (drop the major seventh), C#dim7 (the major seventh becomes a sixth), C#maj7b5 (the minor third becomes a major third), C#m7b5 (the major seventh becomes a flat seventh) or C#mMaj7 (the flat fifth becomes a fifth).
C#mMaj7b5 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On C#mMaj7b5’s sound and use this page follows Robert Rawlins & Nor Eddine Bahha, Jazzology (Hal Leonard, 2005). 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.