A gate-voltage-controlled high transition temperature direct current superconducting quantum interference device (high-T(c) dc SQUID) magnetometer was fabricated to study how the electric field effect affects the device's voltage-flux and voltage-current characteristics. The magnetometer consists of a monolithic YBa(2)Cu(3)O(7-delta) superconducting film and bicrystal junctions covered by a polymethylmethacrylate film as the gate insulator. It was found that the magnetic flux modulated voltage swing of the SQUID magnetometer varies by 48% when the gate voltage is changed from -1.9 to 9.5 V. The variation in voltage swing is attributed to the change of effective capacitance in grain-boundary junctions