If you're relying on HTML forms being filled in to generate queries, the browser will always generate standard query parameters with a question mark and ampersands. But if you're making your own links, you can generate them however you like. Semi-colons should work fine, though you may need to write your one URL parsing functions.

Iirc in java I managed to parse those just fine. Ages ago though.

I also recall actually seeing some web pages somewhere using semicolon, possibly IBM stuff.