Semiconductor devices and methods of forming the same are disclosed. One of the semiconductor device includes an inductor structure, and the inductor structure is on a substrate and includes a first metal layer, a magnetic stack, a polymer layer and a second metal layer. The first metal layer is over the substrate. The magnetic stack is over the first metal layer and has a substantially zigzag shaped sidewall. The polymer layer is over the first metal layer and encapsulates the magnetic stack. The second metal layer is over the polymer layer.