This work discusses the key issues associated with the process development for 200 μm thick structure for mechanically decoupled Silicon on Glass (SOG) MEMS gyroscope. The gyroscope discussed here is a single axis, in-plane moving device with capacitive driving, differential capacitive sensing and has an area of 2.6 × 2.4 cm². Challenges involved in defining masks for High Aspect Ratio (HAR) etching of silicon using Bosch process to a depth of 200 μm through an opening of 8 μm are discussed. The HAR etching of silicon is achieved by using a novel approach of having dual layer masks of Aluminum and photoresist.