Because the semiconductor industry is moving to a larger wafer size and higher process speed, a vacuum pump will be required to have higher pumping speed in bath the viscous and molecular flow ranges. The "gradational lead screw (GLS) pump" unlike these conventional pumps demonstrated the ultimate pressure of 0.0004 Torr and a pumping speed of 8000 L/min over the viscous and molecular flow ranges. The improved performance is attributable to the GLS rotor design. The pump utilizes a small amount of oil. Mass analyzer testing (maximum mass number 120) revealed that there is no evidence of reverse diffusion in the pressure range above 0.002 Torr with a small amount of N-2 gas injected. In summary, the GLS' pump has high pumping speed because of its large intake volume. Electric power consumption is low as a result of its small exhaust volume. By-product is transferred and ejected from the exhaust port through the operation mechanism. The by-product deposition is minimized if the case temperature is maintained above 150 degrees C. Although manufacturing this pump requires a high level of skill, the pump structure is rather simple and the maintenance is easy. Hence it will increase the mean time between overhaul and reduce maintenance cost. A detailed report will be prepared on the characteristics of the GLS, the pump structure, and the performance attributes.