Abstract: Complementary semiconductor devices are fabricated in single crystal semiconductor segments within a monolithic substrate, using planar diffusion techniques. An impurity element of one conductivity-determining type is partially diffused into one of a pair of the single crystal segments having opposite conductivity types to one another. Thereafter, a second impurity element of the other conductivity-determining type and having a faster diffusion coefficient than the first element is diffused into the second of the pair of single crystal segments at a time and for a temperature sufficient to effect penetration of both impurities to substantially the same depth in their respective segments. The concentrations of the impurities are selected to provide common operational element regions of the complementary devices with substantially identical resistivities.