Your question is great for a google search. I searched for 'hottest desert,' and google gave me choices such as 'hottest deserts of the world' and 'hottest deserts of the US,' but I just searched for 'hottest desert.' The first google hit is for the 5 hottest deserts, on a site about how stuff works. I'll check out the hits now, to see if they agree about what is the hottest desert.

OK - the sites seem to agree that the Sahara is the hottest desert. It's also the largest hot desert, but Antarctica is a larger desert; it just isn't hot. Wikipedia says the Arctic is also a larger desert than the Sahara, but of course it isn't hot either.

Wow! Scienceline has answers, too, here: click here to read