YBa2Cu3O7−x/SrTiO3/Au multilayer systems have been prepared insitu by pulsed laser deposition onto (100) SrTiO3 substrates. An electric field controlled device was patterned by suitable metal masks applied successively during the deposition process. The switching time of the superconducting source‐drain channel has been studied at T=4.2 K applying rectangular pulses to the gate electrode. We find that the source‐drain voltage follows the gate voltage variation in accordance with the RC time constant of the device. Our result is consistent with the mechanism of direct charge transfer by the electric field, but inconsistent with a model based on electric field driven migration of the oxygen atoms in the CuO chains of YBa2Cu3O7−x which predicts characteristic times in the order of minutes.