A dielectrically-isolated structure and method of fabricating the same is disclosed wherein the structure includes a layer of silicide which is selectively doped, preferably using an ion implantation process. The doped silicide is then used as the diffusion source for the subsequent formation (through a heat treatment) of various active portions (collector, emitter, drain, source, for example) of a variety of high-voltage, high-speed active devices. The non-doped silicide is advantageously utilized as a low-resistance contact between the buried diffusion region and the surface electrode.