Non-planar transistor

A non-planar transistor is provided. It includes a substrate, a fin structure, a gate structure, a first spacer structure and a source/drain region. The fin structure is disposed on the substrate, the gate structure is disposed on the fin structure. The fin structure includes an upper portion, a concave portion and a lower portion, and the concave portion is disposed between the upper portion and the lower portion. The first spacer structure is disposed on a sidewall of the gate structure. The first spacer structure includes a first spacer and a second spacer, wherein the first spacer is disposed between the second spacer, and a height of the first spacer is different from a height of the second spacer. The source/drain region is disposed in a semiconductor layer at two sides of the first spacer structure.