Some times situation is like we have to parse the string which has both Unicode and ASCII characters in single string, at that time Encoding functions in .NET will not be help ful,
so i have created two usefull functions for that situations...

public static string GetUTF8StringFrombytes(byte[] byteVal)
        {           
            byte[] btOne = new byte[1];
            StringBuilder sb = new StringBuilder("");
            char uniChar;
            for (int i = 0; i < byteVal.Length; i++)
            {
                btOne[0] = byteVal[i];
                if (btOne[0] > 127)
                {
                    uniChar = Convert.ToChar(btOne[0]);
                    sb.Append(uniChar);
                }
                else
                    sb.Append(Encoding.UTF8.GetString(btOne));
            }
            return sb.ToString();
        }

        public static byte[] GetBytesFromUTF8Chars(string strVal)
        {
            if (strVal != string.Empty || strVal != null)
            {
                byte btChar;
                byte[] btArr = new byte[strVal.Length * 2];
                byte[] tempArr;
                int arrIndex = 0;
                for (int i = 0; i < strVal.Length; i++)
                {
                    btChar = (byte)strVal[i];
                    if (btChar > 127 && btChar < 256)
                    {
                        btArr[arrIndex] = btChar;
                        arrIndex++;
                    }
                    else
                    {
                        tempArr = Encoding.UTF8.GetBytes(strVal[i].ToString());
                        Array.Copy(tempArr, 0, btArr, arrIndex, tempArr.Length);
                        arrIndex += tempArr.Length;
                        tempArr = null;
                    }
                }
                byte[] retVal = new byte[arrIndex];
                Array.Copy(btArr, 0, retVal, 0, arrIndex);
                return retVal;
            }
            else
                return new byte[0];
        }