We have studied single-electron turnstile operation in common-gated one-dimensional arrays of four tunnel junctions ͑three dots͒ having inhomogeneous junction capacitances. Analytical calculations show that the source-drain voltage range with a current plateau due to single-electron turnstile operation is increased when the outer two tunnel capacitances are adjusted to be smaller than the inner ones. In fact, we have demonstrated in phosphorous-doped silicon-on-insulator field-effect transistors ͑FETs͒ that back-gate voltage works to assist the turnstile operation, which is primarily ascribed to electrical control of junction capacitance dispersion, i.e., reduction in outer junction capacitances. As a result, postfabrication control of capacitance dispersion in multijunction FETs can be achieved, resulting in successful turnstile operation.