A semiconductor device comprising: an electrically conductive heat sink having a first surface; a semiconductor substrate; a first contact located on a first surface of the substrate, and a second contact located on a second surface of the substrate, wherein the substrate includes a semiconductor region located adjacent to the first surface, the semiconductor region forming a pn junction at an interface between the semiconductor region and the substrate, wherein the first surface of the substrate is mounted on the first surface of the heat sink for electrical and thermal conduction between the heat sink and the substrate via the first contact, wherein the second surface of the substrate is configured and arranged to be mountable on a surface of a carrier, wherein the pn junction located at the interface between the semiconductor region and the substrate forms an active region, the active region being located closer to the first surface of the substrate than the second surface, forming an active surface on the first surface and a passive surface on the second surface, and wherein the electrically conductive heat sink comprises: a first portion extending substantially parallel to a plane containing the first surface of the substrate, wherein the first portion comprises said first surface of the electrically conductive heat sink, a second portion extending away from the first portion of the electrically conductive heat sink for mounting the electrically conductive heat sink on the surface of the carrier; and at least one further portion extending away from the first portion of the electrically conductive heat sink for mounting the electrically conductive heat sink on the surface of the carrier. an electrically conductive heat sink having a first surface; a semiconductor substrate; a first contact located on a first surface of the substrate, and a second contact located on a second surface of the substrate, wherein the substrate includes a semiconductor region located adjacent to the first surface, the semiconductor region forming a pn junction at an interface between the semiconductor region and the substrate, wherein the first surface of the substrate is mounted on the first surface of the heat sink for electrical and thermal conduction between the heat sink and the substrate via the first contact, wherein the second surface of the substrate is configured and arranged to be mountable on a surface of a carrier, wherein the pn junction located at the interface between the semiconductor region and the substrate forms an active region, the active region being located closer to the first surface of the substrate than the second surface, forming an active surface on the first surface and a passive surface on the second surface, and wherein the electrically conductive heat sink comprises: a first portion extending substantially parallel to a plane containing the first surface of the substrate, wherein the first portion comprises said first surface of the electrically conductive heat sink, a second portion extending away from the first portion of the electrically conductive heat sink for mounting the electrically conductive heat sink on the surface of the carrier; and at least one further portion extending away from the first portion of the electrically conductive heat sink for mounting the electrically conductive heat sink on the surface of the carrier. a first portion extending substantially parallel to a plane containing the first surface of the substrate, wherein the first portion comprises said first surface of the electrically conductive heat sink, a second portion extending away from the first portion of the electrically conductive heat sink for mounting the electrically conductive heat sink on the surface of the carrier; and at least one further portion extending away from the first portion of the electrically conductive heat sink for mounting the electrically conductive heat sink on the surface of the carrier.