Unity 配列　配列名.Lengthでエラーが出てしまう

前提・実現したいこと

ゲームオブジェクトを配列から取得してすべてsetactive(False）にしようとしました

発生している問題・エラーメッセージ

配列名.Lengthとしているのに、インデックスが配列の範囲外とエラーが出ます

IndexOutOfRangeException: Index was outside the bounds of the array.

該当のソースコード

c#
1using System.Collections;
2using System.Collections.Generic;
3using UnityEngine;
4
5public class MalingScript : MonoBehaviour
6{
7    
8    public GameObject One;
9    public GameObject Two;
10    public GameObject Three;
11    public GameObject Four;
12    public GameObject Five;
13    public GameObject Six;
14    public GameObject Seven;
15    public GameObject Eight;
16    public GameObject Nine;
17    public GameObject Ten;
18    public GameObject Eleven;
19    public GameObject Twelve;
20    public GameObject Thrteen;
21
22    //　型名　　 配列の名前
23    GameObject[] TrampBox = new GameObject[13];
24
25    // Start is called before the first frame update
26    void Start()
27    {       
28        TrampBox[0] = One;
29        TrampBox[1] = Two;
30        TrampBox[2] = Three;
31        TrampBox[3] = Four;
32        TrampBox[4] = Five;
33        TrampBox[5] = Six;
34        TrampBox[6] = Seven;
35        TrampBox[7] = Eight;
36        TrampBox[8] = Nine;
37        TrampBox[9] = Ten;
38        TrampBox[10] = Eleven;
39        TrampBox[11] = Twelve;
40        TrampBox[12] = Thrteen;
41        TrampBox[TrampBox.Length].SetActive(false); // エラー元
42    }