Thin films of YBa2Cu3O7−x (YBCO) have been prepared on MgO substrates at 650 °C by rf-planar magnetron sputtering using a single oxide target. Depositions at two different substrate positions were examined: (A) above the inner boundary of the erosion area of a target (position A), (B) right above the center of a target (position B). The films deposited at position A suffered a serious deficiency in the contents of Ba and Cu, especially in the low gas pressure region due to the bombardment of the growing films by high-energy particles. Though we could obtain almost stoichiometric films by raising the gas pressure to 15 Pa to reduce the bombardment, high temperature annealing at 950 °C was required to improve their crystallinity and to achieve high critical temperatures (Tc). On the other hand, those deposited at position B were more excellent in crystallinity than those at position A and showed high Tc above 80 K without any annealing. Critical current density C/r) at 77 K was improved from about 103 A/cm2 to about 104 A/cm2 by annealing at low temperature of 500 °C. It is concluded that the deposition with reduced bombardment by high-energy particles enables the fabrication of high Tc YBCO films without a high temperature process.