GDSII

GDSII, short for Graphic Data System II, is a binary file format used to describe integrated circuit layout and mask data. It has served as the de facto standard for exchanging planar semiconductor layouts between electronic design automation (EDA) tools and photomask fabrication facilities. The format concentrates geometric shapes, layer assignment, and hierarchical structure required to define a fabrication mask.

Origins date to the late 1970s and early 1980s at Calma, later integrated into broader EDA ecosystems as the industry standard. Despite its age, GDSII remains widely supported by layout editors and mask writers, and many foundries require or prefer GDSII for mask data handling.

Data model: designs are built from cells (also called structures) that can reference other cells, enabling hierarchy. Geometry primitives include polygons, paths, and text, assigned to design layers and datatypes. Coordinates are integers in user units, and designs are read and interpreted in a hierarchical, stream-based representation. GDSII does not encode color or fill patterns; it encodes geometry only, along with metadata such as cell names and unit resolution.

File organization: the GDSII stream uses a series of records to encode header information, structure definitions, geometry, references, and end markers. Files typically use the .gds or .gdsii extension and are supported by most IC layout tools and mask data prep software.

Usage and impact: GDSII remains central to mask data preparation and exchange in the semiconductor industry. It supports tool interoperability but often requires conversion to newer formats (such as OASIS) for very large designs or advanced features.

Limitations and context: the format is 2D and lacks compression and some modern features. Alternatives and successors, notably OASIS and its variants, provide more compact representations, but GDSII continues to be widely used due to compatibility and legacy workflows.