Abstract: A method of ionizing a liquid is disclosed herein. The method includes the steps of dispensing an electrically conductive liquid onto an electrically conductive membrane so as to form a liquid film on the surface of the membrane, applying an electrical charge to the liquid film on the membrane, generating ultrasonic waves to vibrate the membrane so as to induce capillary waves in the liquid film, and electrostatically attracting the electrically charged crests in the capillary waves so that electrically charged droplets are extracted from the capillary waves and accelerated therefrom for emission. The method is generally utile in various applications including, for example, spacecraft propulsion, paint spray techniques, semiconductor fabrication, biomedical processes, and the like. In addition to the above-described method, an electrostatic colloid thruster for implementing the method is disclosed herein as well.