In the present work, the surface of polyethersulfone (PES) membrane is treated by using tetraethylorthosilicate (TEOS) and trimethylchlorosilane (TMSCl) as grafting agents. Attenuated total reflection infrared spectroscopy (ATR-IR), scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX), atomic force microscopy (AFM), and optical contact angle measurement (OCA) are applied to identify and characterize the membranes. The water contact angle of as high as 150° is obtained for the treated membranes. The modified membranes are examined for desalination using a direct contact membrane distillation setup. Effects of different conditions in membrane preparation as well as operating parameters are investigated. A separation factor of 99.7% and comparable permeate fluxes to those of a commercial polytetrafluoroethylene (PTFE) membrane are obtained.