A semiconductor device includes: a first level detecting circuit for detecting a voltage level at a control terminal after a prescribed time period from when a power supply voltage is supplied to a power supply terminal, a control unit for selecting in which operation mode among a plurality of operation modes the semiconductor device operates, based on a result of detection by the first level detecting circuit; and a regulator for generating an internal power supply voltage based on the power supply voltage supplied to the power supply terminal. The first level detecting circuit and the control unit receive the internal power supply voltage as an operating power supply voltage. In an operation mode, among the plurality of operation modes, where a power supply voltage having a level different from that of a power supply voltage in other operation modes is supplied to the power supply terminal, the control unit performs data processing by using the power supply voltage supplied to the power supply terminal.