The present disclosure relates to a HEMT transistor comprising a first semiconductor layer, a gate arranged on a first surface of the first semiconductor layer, a first passivation layer made of a first material on the sides of the gate, the first passivation layer further extending over a first portion of said surface of the first semiconductor layer, and a second passivation layer made of a second material different from the first material on a second portion of said surface of the first semiconductor layer next to the first passivation layer.