We have fabricated a YBa2Cu3O7 (YBCO) thin‐film dc superconducting quantum interference device (SQUID) with lithographically defined deep‐submicron weak links. At 77 K the voltage response to dc flux is sinusoidal and nonhysteretic, with maximum peak‐to‐peak amplitude of 5 μV. The maximum response is 8 μV at 70 K, where 2LI0/Φ0≊1. At lower temperatures, the maximum response oscillates in the range 4–6 μV. Random telegraph noise was observed near 30–40 K. Well‐behaved Shapiro steps were observable at all measured temperatures below Tc.