A new type of superlattice, semiconductor-atomic superlattice, consisting of multiple periods of semiconductor layers separated by adsorbed atomic/molecular monolayers, requires that the growth remains epitaxial. Specifically, the Si/O superlattices have been fabricated with epitaxially grown thin silicon layers (1-2 nm thick) separated by periodically introduced monolayers of oxygen. High-resolution TEM shows defect density at the Si/O interface is below 10(9)/cm(2) Electroluminescence diodes show a peak in the yellow-green of the visible spectrum, and have been life-tested for over a year without signs of degradation. Measured effective barrier height is between 0.5 and 1 eV. Models of the structures, showing how epitaxy can be continued with a monolayer of oxygen, are presented. Preliminary calculation shows that the strain is relatively low. The door is opened for device applications in silicon optoelectronics.