* Très fatigué (for a male)
* Très fatiguée (for a female)
Here are some other options, depending on the context and desired level of formality:
* Extrêmement fatigué/fatiguée (extremely tired)
* Épuisé/épuisée (exhausted)
* Lassé/lassée (weary)
* Fatigué à mourir (tired to death - informal)
You can also use the phrase "j'ai très sommeil" (I am very sleepy) if you are specifically tired from lack of sleep.