Semiconductor structure with oxide semiconductor layer

The present invention provides a semiconductor structure, including a base, a patterned oxide semiconductor (OS) layer, two source/drain regions, a protective layer, a gate layer and a gate dielectric layer. The patterned OS layer is disposed on the base. Two source/drain regions are disposed on the patterned OS layer and are separated by a recess. Each source/drain region includes an inner sidewall facing the recess and an outer sidewall opposite to the inner sidewall. The protective layer is disposed on a sidewall of the patterned OS layer but is not on the inner sidewall of the source/drain region. The gate layer is disposed on the patterned OS layer, and the gate dielectric layer is disposed between the gate layer and the patterned OS layer.