Disclosed is a one-chip ULSI which can carry out the fixed operation in a wide range of power supply voltage (1 V to 5.5 V). This one-chip ULSI is composed of a voltage converter circuit(s) which serves to a fixed internal voltage for a wide range of power supply voltage, an input/output buffer which can be adapted to several input/output levels, a dynamid RAM(s) which can operate at a power supply voltage of 2 V or less, etc. This one-chip ULSI can be applied to compact and portable electronic devices such as a lap-top type personal computer, an electronic pocket note book, a solid-state camera, etc.