A semiconductor device includes a transistor. The transistor includes a gate electrode, a channel layer, a gate dielectric layer, a first source/drain region and a second source/drain region and a dielectric pattern. The channel layer is disposed on the gate electrode. The gate dielectric layer is located between the channel layer and the gate electrode. The first source/drain region and the second source/drain region are disposed on the channel layer at opposite sides of the gate electrode. The dielectric pattern is disposed on the channel layer. The first source/drain region covers a first sidewall and a first surface of the dielectric pattern, and a second sidewall opposite to the first sidewall of the dielectric pattern is protruded from a sidewall of the first source/drain region.