To simplify \((10^3)^6\) using the Power Rule of Exponents, you multiply the exponents. The Power Rule states that \((a^m)^n = a^{m \cdot n}\).
Applying this rule:
\[ (10^3)^6 = 10^{3 \cdot 6} = 10^{18} \]
Thus, \((10^3)^6\) simplifies to \(10^{18}\).