Biasing is indeed non-trivial, and most designs require temperature compensation to keep drain current constant. In fact, it's pretty easy to fry a GaN part without proper bias sequencing at power-on and off. At least it is with the parts I'm using.

Edit: parts like MAX881R [1] make it pretty easy though :)

[1] http://datasheets.maximintegrated.com/en/ds/MAX881R.pdf