As the level of Si-wafer surface directly affects device line-width capability, process latitude, yield, and throughput in fabrication of microchips, it needs to have ultra precision surface and flatness. Polishing is one of the important processing having influence on the surface roughness in manufacturing of Si-wafers. The surface roughness in final wafer polishing is mainly affected by the many process parameters. For decreasing the surface, the control of polishing parameters is very important. In this paper, the optimum condition selection of ultra precision wafer polishing and the effect of polishing parameters on the surface roughness were evaluated by using central composite designs such as the Box-Behnken method. Moreover, in accordance with variation of process variables, there is a temperature change on pad surface. And so, this paper also researches that this temperature variation affects surface roughness of Si-wafer.