How would i make a point/wave system like this

Hello, I am trying to make a wave system so far i have this code. Which works well and makes it so it adds 5 enemy each wave and does it's job but in the picture bellow there there is art work getting shown every round, on round one it shows a 1 on round two a 2 and so on. How would you go about doing this?

Thanks for your time.

 #pragma strict
 
 var spawnPoints : Transform[];
 var enemyPrefabs : GameObject[];
 
 var yieldTimeMin = 2;
 var yieldTimeMax = 5;
 
 static var enemyCounter = 0;
 
 var spawnXOffsetMin = 0;
 var spawnXOffsetMax = 0;
 
 var spawnZOffsetMin = 0;
 var spawnZOffsetMax = 0;
 
 var defaultSpawnNumber = 5;
 
 var waveNumber = 1;
 
 var isSpawning = false;
 
 function SpawnEnemies(wave : int)
 {
         var spawnNum = (defaultSpawnNumber + 5 * (wave - 1));
         
         isSpawning = true;
         
         for(var i = 0; i < spawnNum;i++)
         {
                 yield WaitForSeconds(Random.Range(yieldTimeMin, yieldTimeMax));
                 
                 var object : GameObject = enemyPrefabs[Random.Range(0, enemyPrefabs.Length)];
                 var position : Transform = spawnPoints[Random.Range(0, spawnPoints.Length)];
                 
                 Instantiate(object, position.position + 
                         Vector3(Random.Range(spawnXOffsetMin, spawnXOffsetMax), 0, 
                                 Random.Range(spawnZOffsetMin, spawnZOffsetMax)), position.rotation);
                 
                 enemyCounter++;
         }
         
         isSpawning = false;
 }
 
 function UpdateWave()
 {
         waveNumber++;
         SpawnEnemies(waveNumber);
 }
 
 
 function Start () 
 {
         SpawnEnemies(waveNumber);
 }
 
 function Update () 
 {
         if(enemyCounter == 0 && !isSpawning)
         {
                 UpdateWave();
         }
 }