The present invention provides a fabrication process that integrates high-aspect-ratio silicon structures with polysilicon surface micromachined structures. In some embodiments the process includes forming an oxide block by etching a plurality of trenches to leave a plurality of vertical-walled silicon structures standing on the substrate, thermally and substantially completely oxidizing the vertical-walled silicon structures, and substantially filling spaces between the oxidized vertical-walled silicon structures with an oxide of silicon to form the oxide block. The process retains not only the high-aspect-ratio silicon structures possible with deep reactive ion etching (DRIE) but also the design flexibility of polysilicon surface micromachining. Using this process, polysilicon platforms have been fabricated, which are actuated by high-aspect-ratio combdrives for many applications such as x-y-z stages and scanning devices. The actuators include an asymmetric combdrive that actuates in torsional/out-of-plane motions, and a high-aspect-ratio combdrive that drives in translational motion.