How do you say you are so hot in french?

"You are very hot". Vous can either mean "you (plural)" or "you (polite singular.)"

Warning. The answer above is strictly correct, but dangerously mis-leading.

J'ai faim, soif, froid(e), chaud(e). -> I amhungry, thirsty, cold, hot

Je suis chaud(e) -> I am horny, sexually aroused.

Vous etes chaud(e) -> You are sexually very attractive, "a hottie" or "a hunk".