A method of designing a semiconductor integrated circuit includes defining a tolerable range in which an operating temperature and an operating power supply voltage of a semiconductor integrated circuit are allowed to vary, computing a target temperature and a target power supply voltage that cancel variation in circuit characteristics caused by process variation of the semiconductor integrated circuit, separately for each circuit characteristic responsive to the process variation, and designing the semiconductor integrated circuit such that the semiconductor integrated circuit properly operates with any temperature and power supply voltage within the tolerable range based on an assumption that the semiconductor integrated circuit is to operate within the tolerable range centered substantially at the target temperature and target power supply voltage.