The advancement of Very Large Scale Integration (VLSI) technology has reduced the size and increased the speed of information processing circuits. Consequently, power supplies for such circuits have had to meet increasing demands for power, yet simultaneously decrease in size. This need for higher power density in the supplies can be met with higher circuit operating frequencies and by using high-density circuit fabrication techniques. Generally, when the conversion frequency of conventional Pulse-Width-Modulated (PWM) supplies approaches 1 MHz, the switching loss becomes very large. This sharply reduces the efficiency of the supply. A quasi-resonant topology reduces much of this loss. For a Zero-Current-Switched (ZCS) Quasi-Resonant Converter (QRC) the turn-off loss is nearly eliminated. It was the objective of the research reported here to combine the quasi-resonant technology with thick-film hybrid microelectronics technology to produce a high density dc-dc converter. For this research endeavor an off-line, half-bridge ZCS-QRC was used. The circuit processed 300V and up to 20A with switching frequencies in the 1MHz to 2MHz range. The voltage and current levels exemplify the high electric field and current densities that must be considered in the design of most QRC circuits that process power up to 100W. Only available materials for thick-film hybrid processing were used although some characteristics were modified. No special magnetic or capacitive components, or semiconductors were developed. To combine technologies the following were performed: 1. identification of critical power electronic circuit and hybrid component parameters such as maximum voltages and currents, thermal and electrical component impedances; 2. assessment of thick-film hybrid microelectronic materials and their compatibility in circuits having high voltage and current levels; 3. development of a complete thick-film power hybrid process; and 4. design, fabrication and evaluation of a power hybrid QRC that has high power-processing density. / Ph. D.