The need for control of molecular contaminants and colloidal particles of 0.2 micron and smaller has resulted from the microelectronics industry's advances into VLSI geometries. Colloidal contamination in the critical rinsing steps prior to high temperature and radiation processing can have a deleterious effect on the properties of these complex devices. Recently, ultrafiltration membrane systems have been developed for point-of-use purification of D.I. rinse water. Ultrafiltration technology, its application and current use in the semiconductor industry, and the effect this technology is having on process cleanliness and device quality will be discussed.