Well, Of course, they are safe, in fact, most of the manufacturers even mention the maximum temperature that their plates can withstand which is generally around 500 degrees so you can be sure they are safe to use. Moreover, it’s always a better idea to use a container or plate that is labeled as microwave safe rather than just putting anything in the microwave cause that definitely won't be safe at all. However, as a precautionary measure, I would suggest you not leave any plate on high heat in the microwave for long periods of time just to be on the safer side:)