Abstruct-We have successfully demonstrated the feasibility of fabricating three-dimensional microstructures by using a combined silicon mold insert and micro hot embossing process (SMIHE).Anisotropic silicon wet etching process has been used to define microstructures on top of a four inch silicon wafer. The whole wafer is then used as the mold insert in a micro hot pressing machine to duplicate plastic microstructures repeatedly. Fine micro pyramid shape microstructures with base width of 30 pm and height of about 21 pm have been fabricated by this method as a demonstration. They have very smooth surfaces and may be suitable for optical applications. This new process shows promise for achieving high yield, reliable fine micro structures on plastic films.