In an example semiconductor device, the voltage/temperature conditions of the semiconductor device and associated calibration codes of multiple instances of ZQ calibrations are pre-stored in a register array. When a pre-stored voltage/temperature condition occurs again, ZQ calibration is not performed. Instead, the associated pre-stored calibration code is retrieved from the register array and provided to the IO circuit. When a voltage/temperature condition of the semiconductor device does not match any pre-stored voltage/temperature condition in the register array, a ZQ calibration is performed. When the ZQ calibration is performed, a register in the register array is selected according to an update policy and updated by the calibration code newly provided by the ZQ calibration along with the voltage/temperature condition at the time when the ZQ calibration is performed.