Random.range within a for loop returns same value everytime.

I have this code, and everytime I run it, it display the same value. It is always 0, 6, 3, 1. What may be the problem?

 public Transform[] SpawnPoints;

 public GameObject[] Trash;

 // Use this for initialization
 void Start () {
     SpawnTrash ();
 }


 void SpawnTrash(){
     for (int i = 0; i < Trash.Length; ++i) {
         int spawnIndex = Random.Range (0, SpawnPoints.Length);
         Instantiate (Trash [i], SpawnPoints [spawnIndex].position, SpawnPoints [spawnIndex].rotation);

         Debug.Log (spawnIndex);
     }
 }