Use the GetString method on the Encoding.UTF8 object.

There're at least four different ways doing this conversion.

1. Encoding's GetString
   , but you won't be able to get the original bytes back if those bytes have non-ASCII characters.

2. BitConverter.ToString
   The output is a "-" delimited string, but there's no .NET built-in method to convert the string back to byte array.

3. Convert.ToBase64String
   You can easily convert the output string back to byte array by using Convert.FromBase64String.
   Note: The output string could contain '+', '/' and '='. If you want to use the string in a URL, you need to explicitly encode it.

4. HttpServerUtility.UrlTokenEncode
   You can easily convert the output string back to byte array by using HttpServerUtility.UrlTokenDecode. The output string is already URL friendly! The downside is it needs System.Web assembly if your project is not a web project.

A full example:

byte[] bytes = { 130, 200, 234, 23 }; // A byte array contains non-ASCII (or non-readable) characters

string s1 = Encoding.UTF8.GetString(bytes); // ���
byte[] decBytes1 = Encoding.UTF8.GetBytes(s1);  // decBytes1.Length == 10 !!
// decBytes1 not same as bytes
// Using UTF-8 or other Encoding object will get similar results

string s2 = BitConverter.ToString(bytes);   // 82-C8-EA-17
String[] tempAry = s2.Split('-');
byte[] decBytes2 = new byte[tempAry.Length];
for (int i = 0; i < tempAry.Length; i++)
    decBytes2[i] = Convert.ToByte(tempAry[i], 16);
// decBytes2 same as bytes

string s3 = Convert.ToBase64String(bytes);  // gsjqFw==
byte[] decByte3 = Convert.FromBase64String(s3);
// decByte3 same as bytes

string s4 = HttpServerUtility.UrlTokenEncode(bytes);    // gsjqFw2
byte[] decBytes4 = HttpServerUtility.UrlTokenDecode(s4);
// decBytes4 same as bytes