Wafer-Level System Integration is integrating complete systems (logic, memory, analog, RF, passives) on single wafer before dicing — maximum integration. Integrated Functions processors, SRAM, DRAM, analog circuits, RF components, resistors, capacitors. Passive Components MIM capacitors on-chip; spiral inductors on metal layers. Integrated resistors (thin-film). Mixed-Signal digital and analog on same substrate; noise isolation critical via separate supplies, guards. RF Integration LNA, mixer, VCO on-chip. Substrate losses, digital noise challenging. Power Management voltage regulators, DC-DC converters, integrated inductors. Efficient power delivery. SRAM/DRAM fast/volatile SRAM for caches; larger DRAM capacity. Both embedded. Non-Volatile Memory flash memory for program storage. Configuration retention. I/O Circuits external communication interfaces; signal level translation. Clock Distribution on-chip PLLs generate clocks; minimize skew, jitter. Power Delivery Network multi-domain supplies; level shifters between domains. Thermal on-chip sensors, DVFS (dynamic voltage frequency scaling). Design Complexity billions of transistors; simulation infeasible at full scale. Sampling/verification strategies. Yield comprehensive testing critical. Multi-project wafers amortize mask cost. WLSI achieves maximum integration merging all system components on silicon.