Methods of forming 3-D integrated semiconductor devices having intermediate heat spreading capabilities

In a method of forming a three-dimensional semiconductor device, a first chip is provided that includes a first substrate, a first device layer positioned on and covering the first substrate, and a first metallization system positioned on and covering the first device layer, wherein the first device layer includes a plurality of first transistor elements. A second chip is also provided and includes a second substrate, a second device layer positioned on and covering the second substrate, and a second metallization system positioned on and covering the second device layer, wherein the second device layer includes a plurality of second transistor elements. The second chip is attached to the first chip so that a heat spreading material is positioned between the first chip and the second chip and covers at least a portion of the first metallization system.