A single-electron turnstile has been demonstrated using a silicon-based dual-gate single-electron transistor (SET). Each gate independently controls the closing and opening of the channel acting as the SET lead, which enables single-electron transfer synchronized with ac gate biases. By applying ac biases to the dual gates with a frequency $f$ of ${\sim}1$ MHz and a phase shift of $\pi$, current staircases quantized in units of ef are observed in drain current vs drain voltage characteristics at 25 K.