Wavelength‐tunable light emission is demonstrated from a planar microcavity employing a deformable‐membrane top mirror. A gold/silicon nitride membrane is suspended by an air gap above a GaAs cavity, containing In0.2Ga0.8As multiple quantum wells, and a GaAs/AlAs distributed Bragg reflector. Micromechanical displacement of the membrane allows for broad and continuous wavelength tuning of the cavity resonance formed by the combination of the semiconductor cavity and the air gap. Optically excited luminescence from the quantum wells is restricted to the resonant cavity modes and exhibits a 31 nm (42 meV) tuning range and 2.2 nm (3 meV) linewidth near 960 nm for 0–15 V applied bias. ©1995 American Institute of Physics.