Abstract: A one-chip semiconductor device comprises a semi-conductor substrate with power supply terminals and data terminals. Formed on the substrate are a clock generating circuit for generating a clock signal when a power supply voltage is applied to it through the power supply terminals, a data processing circuit which is driven by the clock signal to process the data supplied to it through the data terminals, a first voltage detecting circuit for producing a stop signal when it detects that the power supply voltage falls below a first reference voltage, and a second voltage detecting circuit for producing a reset signal when it detects that the power supply voltage falls below a second reference voltage. The stop signal stops the clock generating circuit, whereby the data processing circuit stops and remains in the same condition as is driven by the clock signal. The reset signal initializes the data processing circuit.