In this article, various characteristics of nanoplate FET were studied based on TCAD simulation for a 3-nm node. The optimum geometry specification was proposed through comparison of RC delay from previous studies. Additionally, the impacts of self-heating effects (SHEs) in the 3-nm node were evaluated in the targeting device because it is expected that highly scaled areas such as channels have a negative effect on the performance due to low heat dissipation. This degradation was verified in a single device and in ring oscillator (RO) operation. pMOS is comparatively stronger than nMOS in terms of SHEs due to wider channel width. In RO operation, the influence of SHEs begins to appear at over 0.65 V through power and speed comparison. Therefore, an operation voltage under 0.65 V can be the optimal voltage to suppress SHEs.