The first "dry pumps" based on the Roots/claw principle were launched in 1984 and have made a strong contribution to a revolution in two areas of positive-displacement pumping in the semiconductor industry. These are (a) the clean pumping of systems and load locks and (b) the continuous pumping of processes which generate copious quantities of particulate, condensate or corrosive material as reaction by-products. These pumps are now moving into their third generation. In this paper, the current state-of-the-art is reviewed, with particular reference to methods of achieving ultraclean pumping and to solutions to applications where ~ 100 g/day of particulate (such as aluminium chloride or silica) must be transmitted through the pump with very high reliability. Issues arising from exhaust management of large arrays of pumps, such as those encountered in modern semiconductor fabrication facilities, are also discussed.