not sure what you are trying to do? Does your url contain a querystring param that has questionmarks in it? Not sure if that's even allowed but:
QueryString.GetValue("URL") get's the value of a parameter URL.
So if you had
it would get
But even in case you had:
you would get
If I test with your code I do get the correct values:
Keep in mind the array is 0 based. So your example of  gets the 2nd value!
Not sure if it's just as a test but keep in mind you're now vulnerable for XSS. For example: