A semiconductor transformer includes a first coil inductor and a second coil inductor. The first coil inductor has a first port, a second port and a first coil inductor wall, the first coil inductor wall having a height substantially equal to a thickness of the substrate. The second coil inductor has a third port, a first extension wall connected to the third port, a fourth port, a second extension wall connected to the fourth port and a second coil inductor wall.