The authors have developed a planar field effect device consisting of an artificial grain boundary junction in an Y 1Ba 2 Cu 3O x (YBCO) microbridge which was covered by a 300-nm amorphous SrTiO 3 layer and a 4-mum-wide gate electrode. The layers were grown on Y-ZrO 2 bicrystal. The current transport through the weak link, connecting the superconducting drain and source electrodes, was regulated by the voltage of the insulated gate. Devices with different misorientation angles, thetas, between the two halves of the bicrystal were studied. For 45deg nonsymmetric tilt grain boundaries, the authors observed a strong (more than 50%) enhancement of the supercurrent at positive gate voltage and almost no change, or a slight decrease, at negative voltage. A theoretical model of the device is discussed. At positive gate voltages of 0.5 V and 8 V about 40% and 70% enchancement of the device critical current, respectively, was obtained