**5. Conclusions**

In this paper, we have summarized some of the most relevant challenges for the development of reliable GaN-on-Si vertical trench MOSFETs, for application in power electronics. Specifically, we presented the results of recent case studies, aimed at investigating (a) the origin of OFF-state leakage current, (b) the role of p-body doping in determining the breakdown voltage of the vertical stack, (c) the substantial improvement of reliability that can be obtained through the use of a bi-layer gate insulator, (d) specific failure mechanisms related to the optimization of the trench etching and cleaning procedure, and (e) a set of advanced results on the physics of interface trapping phenomena, obtained through the use of pulsed/transient measurements carried out in dark and under light. The obtained insights help understanding the current issues faced by the GaN for power community, and demonstrates strategies for identifying and analyzing the structural, leakage and trapping constraints to realize efficient and economical GaN-on-Si devices. If the pace of development and innovation within GaN-on-Si technologies is sustained, the benefits could prove to be revolutionary for the power semiconductor industry.

**Funding:** This project has received funding from the ECSEL Joint Undertaking (JU) under grant agreement No. 826392. The JU receives support from the European Union's Horizon 2020 research and innovation programme and Austria, Belgium, Germany, Italy, Norway, Slovakia, Spain, Sweden, Switzerland. This research activity was partly funded by project "Novel vertical GaN-devices for next generation power conversion", NoveGaN (University of Padova), through the STARS CoG Grants call. Part of this work was supported by MIUR (Italian Minister for Education) under the initiative "Departments of Excellence" (Law 232/2016).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** No new data were created or analyzed in this study.

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