<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)>
Private Function SendMessage(ByVal hWnd As IntPtr, _
                             ByVal Msg As UInteger, _
                             ByVal wParam As Int32, _
                             ByVal lParam As String) As Int32
End Function
 
Private Const WM_SYSCOMMAND As System.Int32 = &H112
Private Const SC_CLOSE As System.Int32 = &HF060&
 
SendMessage(Handle, WM_SYSCOMMAND, SC_CLOSE, 0)