Your For Loop is starting at 0 and stepping -2 which isn't helping (the code in the loop never actually executes).
Code:
For i = 0 To bArr.Length - 1 Step -2
The following should help get you started:
vb.net Code:
  1. Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
  2.  
  3.     '   Using a Big Endian Unicode encoding (utf-16BE)
  4.     '     as is required for the desired output format
  5.     Dim enc As Encoding = System.Text.Encoding.GetEncoding("utf-16BE")
  6.  
  7.     '   Encode the string to a byte array
  8.     Dim realStr As String = "السلام عليكم"
  9.     Dim bArr As Byte() = enc.GetBytes(realStr)
  10.  
  11.     '   build the hex string using a StringBuilder
  12.     Dim hexStrBuilder As New System.Text.StringBuilder
  13.     For i = 0 To bArr.Length - 1
  14.         hexStrBuilder.Append(bArr(i).ToString("X2"))
  15.     Next
  16.  
  17.     '   Convert the value of the StringBuilder
  18.     '     to a String value for display
  19.     Dim hexStr As String = hexStrBuilder.ToString
  20.  
  21.  
  22.     '   display the results
  23.     MessageBox.Show(hexStr)
  24.  
  25. End Sub

The above outputs 062706440633064406270645002006390644064A06430645
from "السلام عليكم"