A method of manufacturing a semiconductor device is provided. The method includes forming a fin structure on a semiconductor substrate and forming a well region in the semiconductor substrate by ion implantation so as to form transistors. The transistors include a pull-up transistor, a transfer gate transistor, and a pull-down transistor of a SRAM cell. The ion implantation is used to adjust threshold voltages of the transistors. Standard threshold voltage (SVt) ion implantation conditions are used to adjust a threshold voltage of the pull-up transistor and a threshold voltage of the transfer gate transistor, and low threshold voltage (LVt) ion implantation conditions are used to adjust a threshold voltage of the pull-down transistor.