Which country has the largest percentage of its total territory comprised of desert?

The deserts of Kyzyl-Kum and Kara-Kum (drainage-basin of Syr-Darya river) and the southern Balqash region (drainage-basin of Ile river) are sand deserts (Aral sands) and cover about 47 percent of the territory of Kazakhstan.

The semi-desert that covers the central part of the country (22 percent of the territory) represents the transitional zone between steppe and desert.

So that makes it 70% or semi-arid and arid deserts!

https://en.wikipedia.org/wiki/Geography_of_Kazakhstan

Kyzyl-Kum is in both Kazakhstan and Uzbekistan, Kara-Kum in Turkmenistan. Which country do you mean?

My guess is that Turkmenistan comprises a larger % of desert than Kazakhstan, as the Kara-Kum desert covers almost the total area of this country.