The combination of semiconductor-on-insulator (SOI) substrates with ultrathin Si (or Ge) channel and gate insulator layers opens new opportunities for nonclassical CMOS-compatible devices and possibly optical sources. Unlike their III-V counterparts, which often came first, SOI-based devices have the crucial advantage of potential integrability with dominant silicon technology. We discuss the examples of lateral and vertical tunneling transistors, as well as a tunneling-based SOI intersubband laser. None of these devices has progressed beyond either proof-of-concept demonstrations or, in the case of the intersubband laser, a purely theoretical concept. Still, the unique characteristics deriving from quantum mechanical tunneling make such devices an interesting playground for innovative device research, especially as standard Si CMOS heads towards the rapidly approaching end of scaling. (c) 2007 Elsevier Ltd. All rights reserved.