HtmlTextWriter - problem writing symbols

I am using the below C# routine to generate an .htm file of a dynamically generated page but the trademark TM symbols displays as Ã?¢ââ?¬Å¾Ã?¢ and the copyright as Ã?â??Ã?®.
What needs to be added to get symbols to display instead of their code equivalents?

StringBuilder sb = new StringBuilder();
 StringWriter sw = new StringWriter(sb);
 HtmlTextWriter hw = new HtmlTextWriter(sw);
 base.Render(hw);
 string html = sb.ToString();

            if (mode == 0 )
            {
                using (StreamWriter w = new StreamWriter(new FileStream(Server.MapPath("/SAVE/" + PageID + ".htm"), FileMode.Create)))
                {
  &n ...