High-temperature and high-pressure behaviours of β-Ga2 O3 powder are studied by energy-dispersive x-ray diffraction in a diamond anvil cell (DAC).It is found that the phase transition from the monoclinic β-Ga2O3 to the trigonal α-Ga2 O3 occurs at around 19.2 GPa under cold compression.By heating the powder to 2000 K at 30 GPa,we confirm that α-Ga2 O3 is the most stable structure at the high pressure.Furthermore,the structural transition from β-Ga2O3 to α-Ga2O3 is irreversible.After laser heating,the recrystallized Ga2O3 has a preferable (012)orientation.This interesting behaviour is also discussed.