Large CSV File creator in C#

private  string ExportToCSV(DataTable DataTable, string path)
    {
        string fullpath = "";
        fullpath = path;
        StreamWriter SW;
        SW = File.CreateText(fullpath);
        System.Text.StringBuilder oStringBuilder = new System.Text.StringBuilder();
        foreach (DataColumn oDataColumn in DataTable.Columns)
        {
            oStringBuilder.Append(oDataColumn.ColumnName + ",");
        }
        SW.WriteLine(oStringBuilder.ToString().Substring(0, oStringBuilder.ToString().Length - 1));
        oStringBuilder.Length = 0;
        foreach (DataRow oDataRow in DataTable.Rows)
        {
            foreach (DataColumn oDataColumn in DataTable.Columns)
            {
                oStringBuilder.Append(oDataRow[oDataColumn.ColumnName] + ",");
            }
            SW.WriteLine(oStringBuilder.ToString().Substring(0, oStringBuilder.ToString().Length - 1));
            oStringBuilder.Length = 0;
        }
        SW.Close();
        return fullpath;
    }