A memory system is connectable to a host and comprises a memory chip including a nonvolatile semiconductor memory cell array, a memory controller, a first temperature sensor positioned to measure a first temperature, which is representative of a temperature of the memory controller, and a second temperature sensor positioned to measure a second temperature, which is representative of a temperature of the memory chip. The memory controller is configured to compare the first temperature against a first threshold temperature and a second temperature against a second threshold temperature and carry out access to the memory chip when either the first temperature is greater than the first threshold temperature or the second temperature is greater than the second threshold temperature.