If you go to their website and read about the technologies they can produce p-channel devices, but they don't perform as well as Si. As the below states from their website
Is it also possible to produce p-channel enhancement mode GaN transistors?
Enhancement mode and depletion mode n-channel GaN devices are available on the market today. EPC supplies only enhancement mode n-channel devices at the present time. Whereas it is possible to make a p-channel device, the performance is quite poor compared with silicon. For a preview of EPC’s technology roadmap, watch the video “How to GaN 11: A Look into the Future”. You can also sign up to receive news and product updates from EPC at
http://bit.ly/EPCupdates or by texting "EPC" to 22828.
