A semiconductor integrated circuit having a high withstand voltage TFT and a TFT which is capable of operating at high speed in a circuit of thin film transistors (TFT) and methods for fabricating such circuit will be provided. A gate insulating film of the TFT required to operate at high speed (e.g., TFT used for a logic circuit) is relatively thinned less than a gate insulating film of the TFT which is required to have high withstand voltage (e.g., TFT used for switching high voltage signals).