A U-band oscillator is presented as a divide-by-two direct injection-locked frequency divider (ILFD), with NMOS injection transistors coupled to the LC oscillator. Compared with the both NMOS and PMOS injection transistors, the NMOS only injection transistors contribute to a much wider locking range. The strategy to choose the structure and sizes of the injection transistors for symmetry and the locking range (LR) is briefly introduced in this paper. The oscillator was designed in the 65-nm standard CMOS process, and consumes 4 mW with locking range of 39G-57GHz at 0 dBm injection power.