AbstractDirect trimethylsilylation1)of phenanthrene in different molar ratio of phenanthrene/sodium/trimethylchlorosilane is reported and discussed. Instead of the aromatic silyl compounds, such as 9‐trimethylsilylphenanthrene (V), the hydroaromatic silyl compounds, such as 9, 10–bis (trimethylsilyl)‐9, 10‐dihydrophenanthrene (I) were obtained preferentially. Structure of these compounds are characterized and discussed. These silylated products have a general trend to change their properties during long time storage in the atmosphere under exposure to light. A significant difference of chemical shifts between silylated aromatic compound (V) and silylated hydroaromatic compound (I‐IV) was