A semiconductor device includes a crystal oscillator circuit, a first noise application circuit, and a second noise application circuit. The first noise application circuit is connected to the crystal oscillator circuit and is configured to drive a crystal resonator by selectively applying initial noises of opposite phases to a first external terminal and a second external terminal. The second noise application circuit applies a second noise to the first external terminal by amplifying a signal at the first external terminal and returning the amplified signal to the first external terminal, thereby driving an oscillation amplifier and a crystal resonator of the crystal oscillator circuit and shortening a start-up time of the crystal oscillator circuit.