Recently, new HEMT GaN Normally Off with a buried Player have been developed by the LAAS Laboratory to propose a device adapted to embedded power electronics. In this article, several Normally Off HEMT GaN architectures are compared using TCAD Sentaurus simulation: Gate Recess, P-GaN, and Buried P-GaN. Main failure mechanisms are compared to determine the most robust topology. The new structure with P-GaN Buried shows promising properties with a higher threshold voltage stability.