According to an embodiment, a semiconductor device includes: a first modulation circuit configured to generate a reference signal based on a first clock signal; a second modulation circuit configured to generate a feedback signal with a phase negative relative to a phase of the reference signal based on a second clock signal with a phase negative relative to a phase of the first clock signal; a comparator configured to compare the reference signal with the feedback signal to determine duty and generate a comparator signal; and a driver configured to output a drive signal.