The current‐voltage characteristic at 77 K of a constricted thallium‐based highTcsuperconducting sample exhibits Shapiro steps and is modulated by a dc magnetic field. This device operates as a dc superconducting quantum interference device with a maximum critical currentIcof 350 &mgr;A, a dynamic resistance up to 30 &OHgr;, and a transfer parameter as high as 1.5 mV/&Fgr;0for an estimated inductance of 40 pH. The measured spectral density of the flux noise in the white noise region is 1.4×10−10&Fgr;20/Hz. The 1/fnoise at 1 Hz is 2.1×10−7&Fgr;20/Hz and is reduced by a factor of 10 by a synchronous detection. Implications for thin‐film devices are examined.