Piezoelectric measurements were performed on large single crystals s8 mm along the c directiond of an a-quartz-type piezoelectric material, gallium arsenate, GaAsO4, which allow us to extend the structure-property relationships in the a-quartz-type materials. These first measurements on Y-rotated-cut plates have shown that gallium arsenate is the highest-performance piezoelectric material of this group. As compared to the coupling coefficients of the other materials with the same structure skSiO2 =8%, kAlPO4 =11%, and kGaPO4 =16%d, gallium arsenate exhibits the highest piezoelectric coupling coefficient of about 22%, as has been predicted by the structure-property relationships. Moreover, from these piezoelectric measurements, the C66 8 elastic constant was determined and compared with elastic constants in quartz-type materials. The proposed value for the cut angle of the AT plane in GaAsO4 is 26.3°. In order to extend the previous thermal stability results, thermal gravimetric analysis sTGAd and x-ray diffraction have been carried out on GaAsO4 powder at high temperatures. It has been shown that GaAsO4 is stable up to 1030 °C. The thermal-expansion coefficient of GaAsO4 is 4.0310−5 K−1. The thermal expansion of the predicted AT plane sY −6.3°d in GaAsO4 is shown to be similar to that of the other materials. Finally, it is demonstrated that the intertetrahedral bridging angle u sA-O-Bd of GaAsO4 is the most stable in a-quartz materials, which enables one to predict that GaAsO4 should retain high piezoelectric performances up to 925 °C.