A semiconductor device including a logic transistor, a non-volatile memory (NVM) cell and a contact etching stop layer (CESL) is shown. The CESL includes a first silicon nitride layer on the logic transistor but not on the NVM cell, a silicon oxide layer on the first silicon nitride layer and on the NVM cell, and a second silicon nitride layer disposed on the silicon oxide layer over the logic transistor and disposed on the silicon oxide layer on the NVM cell.