We have studied room‐temperature optical gating of ∼5 ps pulses in GaAs/AlAs microresonators with diameters ranging from <0.5 &mgr;m to 1.5 &mgr;m by using a high‐refractive‐index lens system having a numerical aperture of 1.3. The larger devices exhibited well‐defined transverse modes, which caused decreased modulation of the probe beam. Waveguide dispersion, present in all the devices, showed fair agreement with calculations. The smallest diameter devices (<0.5 &mgr;m) show high modulation, fully recover in <30 ps, and have their peak transmission wavelengths shifted by >500 A˚ compared to a large ∼10 &mgr;m nearby region.