There is provided a phase-switch-equipped variable amplification device including a switch including one input port and two output ports and configured to output a single-ended signal input to the one input port into one of the two output ports, a first converter coupled to the two output ports of the switch and configured to convert the single-ended signal output from the switch into a pair of differential signals having phases different from each other by 180-degree and invert phases of the pair of differential signals in response to a switching operation at the switch, a variable amplifier configured to amplify the pair of differential signals in accordance with a control voltage, and a second converter configured to convert the pair of differential signals amplified by the variable amplifier into a single-ended signal.

According to one embodiment, a semiconductor device includes external terminals supplied with the pair of voltage signals based on a detection result of a resolver through first and second input resistances, respectively, an operation amplifier configured to amplify a potential difference between the pair of the voltage signals supplied to the external terminals, a feedback resistance disposed between an output terminal of the operation amplifier and one of two input terminals thereof, switches disposed between the two input terminals of the operation amplifier and the external terminals, respectively, and a short-circuit failure detection circuit configured to detect whether or not a short-circuit failure has occurred in the resolver based on a voltage level of each of the external terminals in a state where the switches are in an off-state.