I've read just a few books in SciFi genre, never liked it, because it's usually written by writers, not scientists. Though, recently I've read few books written by Peter Watts and Stanislaw Lem. There is actual science in those books, with some speculation, but still: science instead of usual mumbo jumbo. How do I find more of such books? Is it some specific sub-genre?
Yes, there is a term for that. There is a sub-genre called "hard science fiction" (hard-sci-fi) which tends to have real scientific principles at its foundation, and many of which use technical jargon or get very into the details of how their fictional science works practically.
The term is fairly useful for finding authors specifically in that sub-genre, and not just sci-fi authors in general. Aside from the Wikipedia page linked earlier, there's a number of resources and fanpages devoted towards the sub-genre. That is, it's the de facto terminology (in English), for what you're looking for.
Another example, and one that allows me to give a shout out to one of my favorite authors, is the techno-thriller genre, for which Michael Crichton was and is one of the poster children. Some examples of his that most closely fit into the genre:
The Andromeda Strain
The Lost World
Prey (my personal favorite of his)
State of Fear
In a New York Times article published after his death in late 2008, his writing was summed up by the following:
All the Crichton books depend to a certain extent on a little frisson of fear and suspense: that's what kept you turning the pages. But a deeper source of their appeal was the author's extravagant care in working out the clockwork mechanics of his experiments—the DNA replication in Jurassic Park, the time travel in Timeline, the submarine technology in Sphere. The novels have embedded in them little lectures or mini-seminars on, say, the Bernoulli principle, voice-recognition software or medieval jousting etiquette ... The best of the Crichton novels have about them a boys' adventure quality. They owe something to the Saturday-afternoon movie serials that Mr. Crichton watched as a boy and to the adventure novels of Arthur Conan Doyle (from whom Mr. Crichton borrowed the title The Lost World and whose example showed that a novel could never have too many dinosaurs). These books thrive on yarn spinning, but they also take immense delight in the inner workings of things (as opposed to people, women especially), and they make the world—or the made-up world, anyway—seem boundlessly interesting. Readers come away entertained and also with the belief, not entirely illusory, that they have actually learned something.
The writer of this article did a better job of articulating the way in which Crichton transitions from narrative to technological exposition back to narrative; this was a defining feature of his writing.
Tom Clancy is also associated with the sub-genre, but you'd have to ask my dad about that; Clancy's not for me.