A method of forming a semiconductor device includes providing a silicon-on-insulator substrate comprising a semiconductor bulk substrate, a buried insulation layer formed on the semiconductor bulk substrate and a semiconductor layer formed on the buried insulation layer, providing at least one N-type metal-oxide semiconductor gate structure being an NZG gate structure having a gate insulation layer over the semiconductor layer and at least one P-type metal-oxide semiconductor gate structure being a PZG gate structure having a gate insulation layer over the semiconductor layer, the NZG and PZG gate structures being electrically separated from each other.