In this study, we propose a novel structure based on AlGaN substrate or buffer layer to implement a normally-off mode transistor that was difficult to be realized by conventional AlGaN/GaN heterojunction structures. The channel under the gate can be selectively depleted by growing an upper AlGaN barrier with a higher Al mole fraction and a top GaN charge elimination layer on AlGaN substrate or buffer layer. The proposed AlGaN heterojunction field effect transistor can achieve a threshold voltage of > 2 V, which is generally required in power device specification.