Compared to Korea, Thailand is hotter. In comparison with Korea, Thailand is hot. When compared with Korea, Thailand is hot. I don't know if grammatically the other ones are correct, but if I was writting a paper I would say it like that. Thailand is hotter than Korea. Is another way to say it.

They all have the same meaning, just written differently. "Thailand is hotter in comparison to Korea" and "Thailand is hotter in comparison with Korea" seem a bit formal, like something you would write in an essay, and "Thailand is hotter compared to Korea" would be more commonly used in spoken language.