Depends on what you expect them to do exactly. Today’s transistors aren’t much different than older ones, just smaller mainly. People of, say, 20-30 years ago may have the technology to inspect them (electron microscope or something like that), and the knowledge to understand them, but not the equipment to reproduce them.
If you go much farther back in time, say before integrated circuits (1960) or even transistors (1947) were invented, I think it’s unlikely that someone could reverse engineer the thing