In this paper, a sub-THz wireless power transfer (WPT) interface for non-contact wafer-level testing is proposed. The on-chip sub-THz couplers, which have been designed and analyzed with 3-D EM simulations, could be integrated into the WPT to transfer power through an air media. By using the sub-THz coils, the WPT occupies an extremely small chip size, which is suitable for future wafer-testing applications. In the best power transfer efficiency (PTE) condition of the WPT, the maximum power delivery is limited to 2.5 mW per channel. However, multi-channel sub-THz WPT could be a good solution to provide enough power for testing purposes while remaining high PTE. Simulated on a standard 28-nm CMOS technology, the proposed eight-channel WPT could provide 20 mW power with the PTE of 16%. The layouts of the eight-channel WPT transmitter and receiver occupy only 0.12 mm2, 0.098 mm2, respectively.