The phase transformation behavior of hexagonal germanium nitride, including both α- and β-Ge_(3)N_(4), has been studied under shock wave compression. The shock compressed quenched samples indicate phase transformation from hexagonal into a cubic spinel structure (γ-Ge_(3)N_(4)). This transformation is completed with increasing shock pressure up to 40-46 GPa (temperature of 1300-1500 K). The lattice constant of γ-Ge_(3)N_(4) is measured to be 0.82063±0.00019 nm, and the crystal density 6.581 g/cm~(3), by the powder x-ray diffraction. The stability of γ-Ge_(3)N_(4) also has been investigated under shock wave compression. It is found that the spinel structure is very stable, and up to at least 63 GPa (temperature of ～1700 K) there is no indication of the formation of a postspinel phase.
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