AbstractA detailed investigation is made of the Ga3 luminescence spectrum observed in gallium doped silicon after electron irradiation and annealing at ≈ 250 °C. The spectrum exhibits exciton singlet—triplet pair no‐phonon transitions at 0.9291 or 0.9272 eV, respectively, and quasi‐localized modes of vibration energy 10.3, 24.4, and 56.9 meV along with combination modes and lattice phonon bands. An additional higher energy no‐phonon transition is due to an excited exciton state at excess energy of 3.8 meV thermalizing with the singlet—triplet states. The isotropic Zeeman splitting of the triplet (g= 2.00 ± 0.05) shows that the orbital momentum of the excitonic hole is entirely quenched. This and the low thermal dissociation energy of the exciton (16 meV) are used to deduce a strong hole binding energy (≈ 226 meV) whereas the 16 meV energy is attributed to the electron localization. The low electron binding energy is consistent with uniaxial stress measurements which are quantitatively explainable in terms of effective‐mass valley—orbit electron states. This defect represents the first example of a luminescent center in silicon which under uniaxial stress exhibits the whole multiplicity of valley—orbit‐states. The valley—orbit nature of the electron and the quenching of the hole orbital momentum render a symmetry classification