To remove the div tag from being displayed in SPGridView when displaying data from "Multiple Lines of Text" column type, set the HtmlEncode property of the BoundField to false.
BoundField boundfield = new BoundField();
boundfield.HeaderText = "Description";
boundfield.DataField = "Description";
boundfield.SortExpression = "Description";
boundfield.HtmlEncode = false;
m_GridView.Columns.Add(boundfield);