This aim of this dissertation is to fabrication microlens arrays (MLA) by silicon mold using dry etching technique and imprint on the PET substrate by direct imprinting microlens structures on Polyethylene terephthalate (PET) substrates using Si molds.The MLA on PET substrates can be used to increase light emitting efficiency from OLED. The MLA was formed by first etching the silicon wafers using SF6 process gas in an RIE/ECR system using isotropic etching technique.The concave undercuts obtained after the dry etching was removed by wet-etching the wafer in HF and HNO3 solutions.Finally,the fabricated silicon mold was used to imprint the microlens structure on the PET substrates.The microlens array with 10 £gm and 25 £gm radius on PET substrate were successfully fabricated using the technique.The surface coverage of the MLA of beter than 90% was obtained. In addition,the outcoupling efficiency of an OLED can be increased using the MLA.The brightness enhancement factor of 1.67 was achieved using in the MLA comparision to the simulation result of 1.73.