Ion-beam accelerators have been widely used in applications such as medical therapy, ion implantation and nuclear fusion. Compact and low-cost ion-beam accelerator enables wider adoption of these technologies. Multiple-Electrostatic-Quadrupole-Array Linear Accelerator (MEQALAC) has been proposed and has the potential to make a low-cost compact tabletop particle accelerator. Such accelerator needs to be driven by high-frequency power amplifiers that generate high voltages. This thesis provides steady-state modeling, circuit architectures, design methodologies and hardware implementation of an evolution of high-frequency high-efficiency compact switch-mode power amplifiers that generate voltage at kilo-volt scale suitable for MEQALAC. First, Class-D power amplifiers with a novel capacitive shunt branch is proposed and designed which achieves 10kV output voltage with reduced transistor current. Class-E power amplifiers are employed beyond 27-MHz. A widely applicable steady-state model for Class-E inverter is proposed based on Laplace-Based Steady-State Modeling (LBSM) approach. The value of the model is demonstrated by using it to design a finite-input-inductor Class-E inverter with constant output voltage in which the input inductance is selected to resonate with the shunt capacitance enabling constant output voltage and Zero-Voltage-Switching (ZVS) for a range of loading conditions. The proposed approach results in an accurate selection of the value of input inductor with inductor value selection accuracy comparable to simulation. Moreover, a novel geometric optimization approach is proposed to optimize air-core toroidal inductor and improve system efficiency, which achieves 595 quality-factor with 8.4cm diameter at 50-MHz. To improve thermal reliability and operation time in vacuum, a stacked power amplifier architecture using air-core transformer is proposed to combine multiple inverters and extend the thermal limit of the power amplifier. A 27-MHz compact power amplifiers are built based on the proposed architecture and design methodology which generates more than 6kV output voltage from 20V dc input voltage, featuring more than 399 voltage gain, with more than 5% duty ratio in vacuum. Finally, a novel vertically stacked piezoelectric transformer structure with piezoelectric resonator and substrate is proposed. Two generations of prototype piezoelectric transformers are built and tested to verify the proposed structure which achieves 3 – 6 voltage gain at MHz operating frequency with less than 6mm×6mm area and up to 80V voltage rating. The piezoelectric transformers show potential to replace magnetics used in the conventional power amplifiers. Limitations of the prototype piezoelectric transformer voltage rating is discussed which leads to future work. The piezoelectric resonator used in building the piezoelectric transformers is studied in DC-DC power conversion. A merged switched-capacitor piezoelectric-resonator based DC-DC converter is proposed which achieves high efficiency across a wide range of conversion ratio.