Semiconductor device comprising a heterojunction

A semiconductor device with a heterojunction. The device comprises a substrate and at least one nanostructure. The substrate and nanostructure is of different materials. The substrate may e.g. be of a group IV semiconductor material, whereas the nanostructure may be of a group III-V semiconductor material. The nanostructure is supported by and in epitaxial relationship with the substrate. A nanostructure may be the functional component of an electronic device such as a gate-around-transistor device. In an embodiment of a gate-around-transistor, a nanowire ( 51 ) is supported by a substrate ( 50 ), the substrate being the drain, the nanowire the current channel and a top metal contact ( 59 ) the source. A thin gate dielectric ( 54 ) is separating the nanowire and the gate electrode ( 55 A, 55 B)