We describe the use of single substrates as resonators for radio-frequency (rf) superconducting quantum interference devices (SQUID) operation. A standard strontium-titanate substrate with dimensions 10×10×1 mm3 serves as a tank circuit (resonator), a YBCO thin film SQUID washer structure is patterned on it. On the resonator substrate, a small rf washer SQUID with a step-edge junction is positioned in flip-chip geometry, thus forming a magnetometer sensor. This resonator is inductively coupled to the readout electronics. At 77 K, the field sensitivity of this SQUID magnetometer achieved 24 fT/ in the white noise range, 38 fT/ at 10 Hz, and 83 fT/ at 1 Hz.