**4. Conclusions**

We presented the compact 20-W GaN internally matched power amplifier operating from 2.5 to 6 GHz that utilizes a GaN HEMT bare die, single-layer capacitors, and thin-film substrates for input and output matching circuits. The fabricated power amplifier achieved stable operation and flat gain performance by using shunt and series resistors. Under the continuous-wave output power condition, it showed the output power of 43.3–43.9 dBm (21.4–24.5 W), the PAE of 33.4–49.7% and the power gain of 6.2–8.3 dB in the frequency range of 2.5–6 GHz. The developed power amplifier will be e ffectively used in wireless and military applications that require high output power over a wide frequency range.

**Author Contributions:** Conceptualization, D.-W.K.; design, M.-P.L. and S.K.; simulation, M.-P.L. and S.K.; measurement, M.-P.L., S.K., and S.-J.H.; writing, D.-W.K.; supervision and project administration, D.-W.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was partly supported by the Technology Development Program of MSS (S2581160) and the NRF gran<sup>t</sup> of MSIT (2018R1D1A1B07049609).

**Conflicts of Interest:** The authors declare no conflict of interest.
