A semiconductor system includes a semiconductor apparatus and an external apparatus. The semiconductor apparatus includes a calibration code generating circuit, a code shifting circuit, and a main driver. The calibration code generating circuit performs a calibration operation to generate a calibration code. The code shifting circuit changes, based on a shifting control signal, a value of the calibration code. A resistance value of the main driver may be set on the basis of the calibration code and a shifted calibration code. The external apparatus generates the shifting control signal based on the resistance value of the main driver.