Recent results in the field of silicon molecular beam epitaxy (SiMBE) are reviewed. Emphasis is put on the possibility of doping-profile engineering, as in delta-doped layers. Heteroepitaxy of Si1 −xGex on Si is discussed in detail. Due to the band-gap narrowing in the Si1 −xGex several improved devices can be designed, such as heterojunction bipolar transistors and modulation-doped structures which show potential for improved field-effect transistors. An exciting area of research involves superlattices consisting of repetitions of layers of Si and Ge, each with a thickness of only a few atomic layers.