Lack of information is not positive proof to the contrary of that information...
It's doubly dangerous, because 1. it doesn't specify that the pad is connected (however, I would assume by default that it is, particularly because a
standard TO-247 package is specified), and 2. if it IS isolated, the isolation standoff is not specified -- note in the IXYS 'ISOPLUS247' case, it's rated for 2500Vrms. So even if it were isolated, you have absolutely nothing to rely on.
While you can make whatever hand-waving you wish (maybe even buy some and inspect or test them yourself), without #2, you are guaranteed nothing. What's more, the manufacturer is free to change the part under that constraint (or the lack thereof) as they see fit. (Though most datasheets include that nasty little phrase, "subject to change without notice", or something to that effect, making that kind of moot anyway...)
Tim
Intrinsic silicon is not used as an insulator, never has been(?), and never will be. It is impossible in general to use for that purpose.
You may want to update your sources.... We have a process on fully depleted silicon to make very low power (as in quiescent currents) devices. I don't know if this process is used to make power transistors. But it does use a layer if fully depleted silicon because of the electric isolation. FD-SOI fully depleted silicon on insulator. We already have a number of devices i. This process. So does intel and a vunch of others.