D Dominant 7th
7
0 - 4 - 7 - 10Major + minor 7th
About D Dominant 7th
D7 is a small triangle at the top of the neck with a flat seventh added — and the shape is different enough from D major that many players learn it as a separate thing rather than a variation. In the key of G it is the dominant; in a blues in D it is home.
The notes
D, F♯, A, C. The C is the flat seventh, and it sits on the B string at the first fret — the note that changes the whole character. Against the F♯ it forms the tritone that every dominant seventh is built on.
Unlike A7, where a finger is removed from the triad, D7 rearranges the hand entirely: the shape looks like an inverted version of D major, with the fingers redistributed across the same three strings.
On the fretboard
Only four strings sound. The open D provides the root at the bottom, and the low E and A strings are left out — which means the chord sits high and thin compared with G7 or E7.
That thinness is why D7 is often played as a barre at the fifth fret in band settings, and why the open shape belongs to fingerstyle and folk, where the sparseness is an asset.
Where it shows up
As the V7 of G major, the second most common dominant in guitar music after G7 itself. G–C–D7 is a complete song for a large part of the folk repertoire.
In blues in G it takes the same role from the other side, and in a blues in D it becomes the tonic — a chord that never resolves because the form does not want it to.