To make high‐responsivity YBa2Cu3O7−xmicrobolometers with response times in the tens of microseconds, heat capacity and hence physical size must be small. We measured the responsivities and response times of 2.5×2.5 &mgr;m and 10×10 &mgr;m YBa2Cu3O7−xmicrobolometers fabricated on ZrO2substrates and illuminated by an argon‐ion laser focused to a 2 &mgr;m spot. Responsivities were found to be 975 and 700 V/W, respectively, with response times of 10 and 40 &mgr;s.