We report on an electro-optic modulator fabricated from a silicon slot waveguide and clad in a nonlinear polymer. In this geometry, the electrodes form parts of the waveguide, and the modulator driving voltage drops across a $120\mathrm{nm}$ slot. As a result, a half wave voltage of $0.25\mathrm{V}$ is achieved near $1550\mathrm{nm}$ . This is one of the lowest values for any modulator obtained to date. As the nonlinear polymers are extremely resistive, our device also has the advantage of drawing almost no current, suggesting this type of modulator could operate at exceedingly low power.