you could use regex:

vb Code:
  1. Dim testStr As String = "SHG9001233 SHG9001234 SHG9001235"
  2. Dim rx As New Regex("[A-Z]{3}\d+")
  3.  
  4. For Each m As Match In rx.Matches(testStr)
  5.     MsgBox(m.Value)
  6. Next

don't forget to import regex:

vb Code:
  1. Imports System.Text.RegularExpressions