The atomic and electronic structures of the B/Si(100) surface have been studied using high-resolution core level and valence band photoelectron spectroscopy as well as low energy electron diffraction. The structure models for such a surface have been proposed, which consist of boron atoms residing on the top surface adatom sites. Experimental evidence shows that this surface is not a dangling bond-free surface. Epitaxial growth of Si and Ge on this structure has been achieved at relatively low temperature, and our results indicate that boron atoms underneath the epitaxial layer act as acceptors. As a result, conversion of an n-type to p-type region takes place near the surface. Comparison of this surface with the other group-III metals on Si(100) surface has also been conducted.