A semiconductor memory device with low power consumption and improved transfer rate of an input/output buffer at reduced manufacturing cost is provided. Thick-film transistors are used for a memory cell array 33, a row decoder 30, and a sense amplifier 32, surrounded by a bold broken line. Thick-film transistors having a threshold voltage lower than the aforementioned transistors are used for input buffers 11 to 13 and an input/output buffer 26, surrounded by a bold line. Thin-film transistors are used for a clock generator 16, a command decoder 17, a mode register 18, a controller 20, a row address buffer and refresh counter 21, a column address buffer and burst counter 22, a data control circuit 23, a latch circuit 24, a DLL 25, and a column decoder 31.