Provided are a gate-all-around (GAA) complementary metal oxide semiconductor (CMOS) and a fabrication method thereof. The GAA includes an nMOS and a pMOS. The nMOS includes a first channel region and a first gate electrode formed on a semiconductor substrate, and the pMOS includes a second channel region and a second gate electrode formed on the semiconductor substrate, where the first channel region and the second channel region are formed of semiconductor materials with the same conductivity type, and the first gate electrode and the second gate electrode are formed of the conductive materials with the same work function. This GAA CMOS reduces the processing steps for fabricating the GAA CMOS, thereby reducing the process complexity and the production cost, which is beneficial for improving the performance and reliability of CMOS and its integrated circuits.