VLSI (Very Large-Scale Integration) is the process of creating an integrated circuit (IC) by combining millions of transistors or devices into a single chip. Before the introduction of VLSI technology, most ICs had a limited set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM, and other glue logic. VLSI lets IC designers add all of these into one chip.
At one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like ultra-large-scale integration (ULSI) were used. But the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are no longer in widespread use.
However, with increasing VLSI complexity, an alternative strategy that has evolved is to design in testability at the design stage instead of evolving a test strategy at a later stage for a designed product.
VLSI is dominated by the CMOS technology and much like other logic families, this too has its limitations which have been battled and improved upon since years.