A new gallium isomorph of the two-dimensional fast ion conductor, β-Al2O3, Zn-doped K-β-gallate, has been grown by K2O vaporization from K2OGa2O3 melts. A crystal of composition (K2O) (0.812ZnO) (6.126Ga2O3) with ≅68% excess K+ over the stoichiometric composition is typical from a melt with 4% added ZnO. This crystal has all of the charge of the excess alkali compensated by the negative charge on a zinc center in the spinel block and, hence, has no interstitial oxygens in the conduction plane, as is the case with β-Al2O3 and Na-β-gallate. The log σT vs 1/T plot shows a distinct change of slope at 300°C. No corresponding specific heat anomaly could be observed. There is a change in slope in the temperature dependence of two low-energy Raman modes near the same temperature, however. When the K+ is replaced by Na+ by ion exchange, the resulting log σT vs 1/T plot is linear over the entire measured temperature range, and the Raman spectrum reduces to a single, temperature-independent, low energy mode. © 1981.