Direct synthesis of K-beta- and beta "-gallates by Ga2O3-K2O solid-state reaction is described. The formation of K-beta- or beta "-gallates depends on the initial Ga2O3 phase. alpha-Ga2O3 leads to K-beta-gallate; beta-Ga2O3 leads to K-beta "-gallate. K-beta "-Gallate is stable < 1200 degrees C. The high temperature stability of K-beta "-gallate can be enhanced by doping with aliovalent ions.