Yes, it is spelt Техас in Russian (stress on А). I am not sure, but I guess it is because "Texas" is originally a Spanish name, and it is pronounced that way (with "hard" [х]) in Spanish.
Someone might have to correct me.
Similarly, the word "Mexico" sounds [Мэхико] in Spanish. Quite illogically, in Russian it is spelt Мексика when referred to the country, and Мехико when referred to its capital. The first vowel (Е) is stressed in either name.