A semiconductor memory device includes a thermosensor that senses present temperatures of the device and confirms whether the temperature values are valid. The thermosensor includes a temperature sensing unit, a storage unit and an initializing unit. The temperature sensing unit senses temperatures in response to a driving signal. The storage unit stores output signals of the temperature sensing unit and outputs temperature values. The initializing unit initializes the storage unit after a predetermined time from an activation of the driving signal. A driving method includes driving the thermosensor in response to the driving signal, requesting a re-driving after a predetermined time from the activation of the driving signal, and re-driving the thermosensor in response to the driving signal input again.