It *gets* the hottest. In summer, it has record high temperatures. In winter, even the nearby Sonoran desert will be warmer than Death Valley.
The high temperature is due to a combination of the low elevation (higher atmospheric pressure) and extremely dry conditions allowing for high insolation ("insolation" being sunlight).
A low-lying area in lee of mountains will often experience higher temperatures due to foehn wind, and it gets stronger the bigger the elevation difference. In addition, lower-lying areas tend to be hotter due to an amplified greenhouse effect.
There's also some peculiarity with the shape of the valley sort of trapping the air and hampering the convection that would normally spread more of the heat upwards. How much that depends on the low elevation of the valley I'm not sure.
Death Valley is in the great basin “Rift Valley”.
A rift valley is a place where the earths crust is stretching, and therefore thinning.
This particular rift is bordered by the Sierras and the Wasatch.
DV is right where the Sierras are rising up as the rift stretches out. It seems to be the riftiest place in the Rift Valley in part because the basin rifts more to the south, (it goes from Oregon to the Colorado river).
DV is a hole. A place where the crust pulled off of the big Sierra crust and went with the eastern crust. Then it filled with debris. It’s one of the places where the earths crust is the thinnest and may one day get filled in by a magma volcano.
Not a coincidence. Although there are other factors that combine to make that particular place hot, altitude is a big part of it. The higher you go in the atmosphere the less insulating atmosphere their is above our preventing the heat from radiating into space. That is why the tops of many mountains are cold and snowy when the base is warm. The lower you go the warmer it gets. As the thicker the insulating blanket of atmosphere is on top of you.