The foundry development of integrated photonics has revolutionized today’s optical interconnect and datacenters. Over the last decade, we have witnessed the rising of silicon nitride (Si3N4) integrated photonics, which is currently transferring from laboratory research to foundry manufacturing. The development and transition are triggered by the ultimate need for low optical loss offered by Si3N4, which is beyond the reach of silicon and III-V semiconductors. Combined with modest Kerr nonlinearity, tight optical confinement, and dispersion engineering, Si3N4 has today become the leading platform for linear and Kerr nonlinear photonics, and it has enabled chip-scale lasers featuring ultralow noise on par with table-top fiber lasers. However, so far all the reported fabrication processes of tight-confinement, dispersion-engineered Si3N4 photonic integrated circuits (PICs) with optical loss down to few dB/m have only been developed on 4-inch (100 mm diameter) or smaller wafers. Yet, to transfer these processes to established CMOS foundries that typically operate 6-inch or even larger wafers, challenges remain. In this work, we demonstrate the first foundry-standard fabrication process of Si3N4 PICs with only 2.6 dB/m loss, thickness above 800 nm, and near 100% fabrication yield on 6-inch (150 mm diameter) wafers. Such thick and ultralow-loss Si3N4 PIC enables low-threshold generation of soliton frequency combs. Merging with advanced heterogeneous integration, active ultralow-loss Si3N4 integrated photonics could pave an avenue to addressing future demands in our increasingly information-driven society.