Spinel Mg(Al1-xGax)(2)O-4 (x=0-1) solid solutions were synthesized via solid-state method. Replacement of Al3+ by Ga3+ in MgAl2O4 gave rise to the expansion of the lattice, as well as blueshifts of FT-IR and Raman peaks. The homogeneous solid solutions, high relative densities, large grain sizes, and compact microstructures resulted in excellent microwave dielectric properties for spinel Mg(Al1-xGax)(2)O-4 (x=0.6) ceramics sintered at 1485 degrees C: that is, epsilon(r)=8.87, Qxf=107000GHz (at 14.8GHz), and (f)=-16ppm/degrees C. Spinel-structured Mg(Al1-xGax)(2)O-4 (x=0-1) solid solutions possessed low sintering temperatures, wide temperature regions (similar to 100 degrees C), and small negative (f) values. These outstanding performance make Mg(Al, Ga)(2)O-4 a promising candidate material for millimeter-wave devices.