Here's 2 cents:
OK, well I'll assume that you've studied transistors already, at least BJTs.
If you're doing searching, researching, and learning, you might want to look at thyristors, especially if you're interested in power switching. You can start with SCRs, then Triacs, Quadracs, and Alternistors. It's interesting to learn how to get them to do what you want them to do, and importantly, prevent them from doing what you don't want them to do. (Also search on snubbers and dv/dt.)
Oh, and then you can move on to IGBTs.
Good luck, and enjoy!