This disclosure is directed to a complementary metal oxide semiconductor (CMOS) transistor that includes a gallium nitride n-type MOS and a silicon P-type MOS. The transistor includes silicon 111 substrate, a gallium nitride transistor formed in a trench in the silicon 111 substrate, the gallium nitride transistor comprising a source electrode, a gate electrode, and a drain electrode; a polysilicon layer formed on the gallium nitride transistor, the polysilicon layer coplanar with a top side of the silicon 111 substrate; a first metal via disposed on the source electrode; a second metal via disposed on the gate electrode and isolated from the first metal via by a polysilicon layer; a first trench contact formed on the first metal via; and a second trench contact formed on the second metal via; the first trench contact isolated from the second trench contact by at least one replacement metal gate (RMG) polysilicon island.