It could be any power device, if the packaging requires it.
There is a type of packaging used for extremely high power devices called appropriately 'hockey puck' packaging. The device is built as a squat cylinder with the two faces each being electrodes/heat sink connections.
Additional electrodes are made available at the side of the devices.
I've only seen SCRs and vacuum tubes packaged this way, but anything is possible.
See figure 3 here:
http://www.darrahelectric.com/trouble.htm -Jon
