An enhancement-mode transistor and method for forming a gate of an enhancement-mode transistor are provided. The method includes: (a) providing a p-doped AlxGayInzN gate layer, consisting of a first part and a second part on top of the first part, above a p-doped Alx′Gay′Inz′N channel layer of an enhancement-mode transistor under construction; and (b) providing a metal gate layer on the top surface of the second part, the metal gate layer being formed of a material such as to form a Schottky barrier with the second part, wherein providing the p-doped AlxGayInzN gate layer comprises the steps of: (a1) growing the first part above the p-doped Alx′Gay′Inz′N channel layer of the enhancement-mode transistor under construction, the first part having an average Mg concentration of at most 3×1019 atoms/cm3, and (a2) growing the second part on the first part, the second part having an average Mg concentration higher than 3×1019 atoms/cm3 and having a top surface having a Mg concentration higher than 6×1019 atoms/cm3.