A 3D stacked parallel-parallel power combiner includes first and second parallel power combining transformers and a first parallel power combiner. The first parallel power combining transformer includes first and second primary windings receiving first and second input signals, and a first secondary winding coupled to the first and second primary windings and providing a first output signal based on the first and second input signals. The second parallel power combining transformer includes third and fourth primary windings receiving third and fourth input signals, and a second secondary winding coupled to the third and fourth primary windings and providing a second output signal based on the third and fourth input signals. The first parallel power combiner is connected to output terminals of the first and second parallel power combining transformers and provides a third output signal by combining the first and second output signals.