Death when a character hits the ground from a certain height

I'm trying to make my character die when they hit the ground from a height of 4. Can some please help me out I know I'm on the right path, but I can't figure this part out.

 public Transform playerPos;

 // Update is called once per frame
 void Update () {
     if (playerPos.position.y > 4)
         yield return new WaitUntil(playerPos.position.y = 0);
             print("player had died");
 }

please help me.