the present invention provides a self - refresh period adaptable for testing cells that are weak against hot temperature stress . an apparatus for controlling a self - refresh operation in a semiconductor memory device includes a first period selector for generating one of a period - fixed pulse signal having a constant period and a period - variable pulse signal having a variable period based on a temperature of the semiconductor memory device in a test mode ; and a self - refresh block for performing the self - refresh operation in response to an output of the first period selector .