Gallium(I) oxide, digallium monoxide or gallium suboxide is an inorganic compound with the formula Ga<sub>2</sub>O.
Gallium(I) oxide can be produced by reacting gallium(III) oxide with heated gallium in vacuum:
It can also be obtained by reacting gallium with carbon dioxide in vacuum at 850 ðC.
Gallium(I) oxide is a by-product in the production of gallium arsenide wafers:
Gallium(I) oxide is a brown-black diamagnetic solid which is resistant to further oxidation in dry air. It starts decomposing upon heating at temperatures above 500 ðC, and the decomposition rate depends on the atmosphere (vacuum, inert gas, air).