Three dimensional microstructures have been made on glass substrates using surface micromachining techniques. Bridge structures were fabricated using both hydrogenated amorphous silicon and microcrystalline silicon. A low density silicon nitride with an etch rate of 100 Å/s in buffered HF was used as the sacrificial layer. As an example of how micromachining can be applied to large area electronics, thin film transistors (TFT) with the dielectric replaced by an air-gap were fabricated. The electrical characteristics of the first working devices are presented.