Provided are a semiconductor memory device and a memory system including the same, which may calibrate a level of an output voltage in consideration of channel environment and a mismatch in on-die termination (ODT) resistance of a memory controller. The memory system includes a memory controller and a semiconductor memory device. The semiconductor memory device is configured to generate a reference voltage based on driving information of the memory controller, and calibrate an output voltage level based on a reference voltage when the semiconductor memory device is electrically connected to the memory controller.