Semiconductor device and method for fabricating a semiconductor device

A method for fabricating a semiconductor package, the method comprising:

• providing a substrate comprising an insulation layer, the insulation layer comprising a first upper main face and a second lower main face opposite to the first upper main face;
• providing a leadframe comprising a first upper main face and a second lower main face opposite to the first main face;
• arranging a semiconductor transistor die on the first main face of the leadframe;
• applying a joint layer on one or both of the second lower main face of the leadframe or the first upper main face of the insulation layer, the joint layer being formed by diffusion soldering or diffusion sintering from at least one source material with at least one first transition temperature, wherein after the forming, the joint layer has a second transition temperature higher than the first transition temperature;
• connecting the leadframe to the substrate by performing a melting and subsequent reflow process;
• and
• applying an encapsulation covering an inner portion of the leadframe, the semiconductor transistor die, and the insulation layer.