We have fabricated coplanar type dc SQUIDs using NdBa2Cu3Oysuperconducting thin films and operated fundamental single‐flux‐quantum (SFQ) circuits. The Josephson junctions were made by the narrow‐focused ion beam irradiation technique. For a 145 &mgr;m wide and 10 &mgr;m long logic SQUID having a critical current of 105 &mgr;A and an inductive parameter (&bgr;L) of 28, a store and a restore of the flux quantum have been demonstrated at temperatures of 4.2–30 K. These operations were performed with an input pulsewidth of 5 ns (5 ns was the shortest input pulse width available from our function generating equipment). These results show experimentally the possibility of high speed operation in all high‐Tcsuperconducting digital circuits. ©1996 American Institute of Physics.