procedure TForm1.StayOnTopClick(Sender: TObject);
begin
    if StayOnTop.Checked then
    begin
        Form1.FormStyle := fsStayOnTop;
   end
  else
   begin
       Form1.FormStyle := fsNormal;
      StayOnTop.Checked := False;
   end;
end;
An example from Clayton Turner

REAL Stay On Top..

Windows real StayOnTop procedure and reverse

//StayOnTop mode
    SetWindowPos(handle, hwnd_TopMost,0,0,0,0, swp_NoMove or swp_NoSize)

//Normal Mode
    SetWindowPos(handle, hwnd_NoTopMost,0,0,0,0, swp_NoMove or swp_NoSize);