To simplify \((10^3)^6\) using the Power Rule of Exponents, you can apply the rule that states \((a^m)^n = a^{m \cdot n}\).
In this case, you have:
\[ (10^3)^6 = 10^{3 \cdot 6} \]
Now calculate \(3 \cdot 6\):
\[ 3 \cdot 6 = 18 \]
So, it simplifies to:
\[ 10^{18} \]
Therefore, \((10^3)^6 = 10^{18}\).