A hetero-structure field effect transistor (HFET). The HFET may include a first contact and a second contact and a hetero-junction structure. The hetero-junction structure may include a first layer made from a first semiconductor material and a second layer made from a second semiconductor material. An interface at which the first layer and the second layer are in contact with each other may be provided, along which a two dimensional electron gas (2DEG) is formed in a part of the first layer directly adjacent to the interface, for propagating of electrical signals from the first contact to the second contact or vice versa. The transistor may further include a gate structure for controlling a conductance of the channel; a substrate layer made from a substrate semiconductor material, and a dielectric layer separating the first layer from the substrate layer. The second contact may include an electrical connection between the substrate layer and the first layer. The electrical connection may include a passage through the dielectric layer filled with an electrically conducting material which is electrically connected to the first layer.