Beryllium Oxide, commonly called Beryllia, and developed in the 1950s as a space-age technical ceramic material, offers a uniquely desirable combination of properties which are not found in any other ceramic material.   Distinguished by its excellent thermal conductivity, it is an ideal material for applications requiring large heat dissipation as well as dielectric and mechanical strength.   It is particularly well suited for use as a diode laser and semiconductor heat sinks and as a rapid thermal transfer medium for miniaturized circuitry and tightly contained electronic assemblages.