My 5 year old constantly yells at the top of his lungs: Advice?

I have an almost five year son who is constantly yelling at the top of his lungs. Especially in our 9mo daughter’s face. I don’t know what to do anymore! I don’t wanna yell at him cuz I feel like it will make him be mean to his little sister, but how can I make him understand that it’s not OK? TIA