Compared to vacuum electron devices, solid-state RF technology for powering particle accelerators offers significant improvements in terms of operating lifetime (> 1 million hours), efficiency (>70%) and availability. However, commercially available 50 V RF Gallium Nitride (GaN) and Silicon LDMOS technology achieve only 1 - 1.5 kW building blocks in CW operation for VHF frequencies, and lower power levels at UHF and higher frequencies which are of interest to the particle accelerator community. Thus, power combining of hundreds to thousands of modules is required to achieve hundreds of kilo-watts to mega-watts power level; this approach adds complexity and degrades efficiency which limits its applicability in mega-watts class systems.This publication introduces an emerging solid-state technology based on RF GaN/SiC High Electron Mobility Transistors (HEMT) designed to operate at 100 VDC in CW mode and up to 150 V in pulse mode. More specifically, demonstration 50 mm single die devices are reported here which achieve 600 W CW at 100 V with 80% efficiency and 1-kW at 145 V bias with a pulse width of 100 µs and 10% duty cycle, also with 80% efficiency. A comparison between CW and pulse operation with 100 µs pulse width 10% duty cycle and 10 ms 10% signals is reported. The design employs harmonic tuning for class E, F or inverse F power amplifier topology to achieve >70% efficiency and assembly techniques that overcome heat dissipation in such high-power density systems. These devices and the respective circuits have been designed to operate at 325 MHz and 650 MHz, with potential applications at other UHF frequencies and L-band. The technology allows for single-ended transistors and small modules as building blocks with a power level of 5 - 10 kW and efficiency >70% which reduce the required number of combiners and related losses to achieve mega-watt power levels. The emerging technology developed for high efficiency high-power RF sources in particle accelerators can also be applied in other industrial, scientific and medical (ISM) applications, as well as in radars for aerospace and defense applications, whenever kilo-watts to mega-watts RF power is required. The high efficiency and longer lifetime of these solid-state devices translate into fewer replacements and reduced electrical power consumption for lower maintenance and operating cost. High modularity also ensures no down-time during maintenance.