This paper describes the design, construction, and evaluation of a three-dimensional (3D) ultrasound system to be used for tumor treatment using high-intensity focused ultrasound (HIFU). The system consists of two parts: an ultrasonic therapy part and a treatment planning part. The ultrasonic therapy part consists of an ultrasound bowl-shaped transducer made from lead zirconate titanate (PZT) and with a resonance frequency of 0.5 MHz. Electrical LC matching circuit built for maximum electrical power delivery to the transducer, a function generator, and a power amplifier. The ultrasonic therapy part is designed for generating a focus with high acoustical powers. The treatment planning part consists of three stepper motors (responsible for moving the setup in the x- y- and z-directions), three high-voltage high-current Darlington arrays (to supply the stepper motors with the required voltages and currents), and C# software to perform the treatment planning. To assess the movement of the treatment planner, each of the three stepper motors was moved forward and backward from end to end. Then the treatment planner was successfully driven to cover cubes of dimensions of 1 × 1 × 1 cm3, 2 × 2 × 2 cm3, 4 × 4 × 4 cm3, and 8 × 8 × 8 cm3, with step sizes 0.5 mm, 1 mm, 2 mm, and 4 mm, respectively. Ex vivo experiments were performed and indicated the capability of the system to generate lesions both on- and off-axis. Three different lesions, one on-axis and two off-axis, were successfully generated.