We experimentally demonstrate active tuning of an ultracompact silicon-on-insulator trapezoid Fabry-Pérot resonator having a volume of 5.31 μm3. We show that the ultrafast nonlinear dynamics arising from two-photon and free-carrier absorption can be used to achieve a signal attenuation of 66% in the device, and the changes in the steady-state resonant properties of the device resulting from the thermo-optic effect induce a large red-shift in its resonance of Δλ = 7.57 nm. It is envisaged that the insight gained from this class of device will be valuable in the integrated optics community as ultrafast modulators, and switches are designed to occupy smaller volumes.