A new surface micromachining method based on porous silicon formation followed by electropolishing is presented in this paper. It generates in a single electrochemical etch step a plate of porous silicon, releases it from the substrate without using a sacrificial layer and lifts it out of plane. The plate can be rotated by a thermal bimorph actuator. Large, flat, astuatable flip-up plates of porous silicon have been realized with a typical thickness of 30 mum and areas ranging from 250 mum by 750 mum to 2400 mum by 4000 mum. They can be turned by up to 90 degrees in the DC mode and show resonances at 60 Hz to 3 kHz, depending on the size. Its applications are microoptical systems like scanner mirrors or tunable optical filters. Layer density modulations in the porous silicon plate give an interference filter that can be tuned by tilting and serve as microspectrometer. The wavelength resolution is less than 20 nm in the visible.