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Electrically tunable mid‐infrared metasurfaces with nanosecond response time and broad tuning range are reported. Electrical tuning is achieved by employing strong polaritonic coupling of electromagnetic modes in metallic nanoresonators with voltage‐tunable inter‐subband transitions in semiconductor heterostructures, tailored for a giant quantum‐confined Stark effect. Experimentally, a 220‐nm‐thick multi‐quantum‐well semiconductor layer is sandwiched between a ground plane and a metal layer patterned with plasmonic nanoresonators. Approximately 300 nm absorption peak tuning and over 30% absorption change are demonstrated at around 7 μm wavelength at normal incidence by changing the DC bias voltage from 0 to +5 V. Fast reflectivity modulation of the metasurface is shown with a response time less than ∼10 ns using bias voltage modulation between +2 V and +4 V. Since the bias affects the optical response at the individual nanoresonator level, this approach may be used to create metasurfaces for ultrafast electrical wavefront tuning and beam steering. [ABSTRACT FROM AUTHOR]