A semiconductor device includes a fin structure for a fin field effect transistor (FET). The fin structure includes a base layer protruding from a substrate, an intermediate layer disposed over the base layer and an upper layer disposed over the intermediate layer. The fin structure further includes a first protective layer and a second protective layer made of a different material than the first protective layer. The intermediate layer includes a first semiconductor layer disposed over the base layer, the first protective layer covers at least side walls of the first semiconductor layer and the second protective layer covers at least side walls of the first protective layer.