As microelectromechanical systems become more complex, designers will find it useful to derive models of the geometry of their device structures directly from the process description and planar mask patterns. OYSTER simulates the geometric effects of sequential IC process stages, including patterning of photoresists with planar masks, in order to produce three-dimensional polyhedral representations of all material structures in a design cell after each process stage. The polyhedral models may be used with various analytic procedures as sources of geometric data for finite-element calculations, or they may be subjected to interference calculations, or inspected to detect structural anomalies. OYSTER has been developed for IC simulation, but is applicable to microelectromechanical systems manufactured using similar processes. In addition, because it uses basic functions of a solid modeling program developed for mechanical systems, it provides access to features like dimensioning and tolerancing and kinematics. © 1989.