Gallium nitride (GaN)-based digital integrated circuits (ICs) are constructed on the commercially available GaN-on-Si wafer designed for pGaN gate HEMT. The functions of inverter, NAND, AND, NOR, and OR logic circuits are successfully realized based on direct-coupled field-effect transistor logic (DCFL) structure. Under a drive voltage of 5V and a load ratio of 20, the low output (VOL) can reach as low as 0.1V. Additionally, a functional-oriented driver, a SR flipflop, and a NOR gate D flipflop are constructed. All the transient tests at a frequency of 100 kHz and temperatures up to 200 °C exhibit satisfying performance characteristics.