In this paper, an all-digital and high-resolution transmit-beamforming circuit for high-frequency ultrasound imaging systems is presented. Conventional transmit-beamformers are typically implemented via field programmable gate arrays (FPGAs). However, the delay resolution and chip size of FPGAs is unable to meet the requirements of high-frequency and portable ultrasound imaging systems. The proposed transmit beamformer comprises an all-digital delay-locked loop (ADDLL) and a beamforming delay line (BDL). The proposed digitally-controlled delay cell in ADDLL and BDL comprises a ladder-shaped delay stage and an interpolation delay stage, which extends the delay range and improves the delay resolution, respectively. The proposed transmit beamformer is implemented in 0.18 μm CMOS technology and integrated with a 30-MHz high-frequency linear array. The simulation results show that each channel can be programmed to achieve a maximum time delay of 439 ns with a resolution of 441 ps. In addition, the lateral resolution at 5, 7.5, and 10 mm is 39.2, 43.4, and 60.1 μm, respectively.