Solution:

$\begin{aligned}\\ & \sum_{n=-\infty}^{\infty}|h(n)|\lt\infty \\\\ & =\sum_{n=-\infty}^{\infty}\left|\left(\frac{1}{2}\right)^n u(n)\right| \\\\ & =\sum_{n=0}^{\infty}\left(\frac{1}{2}\right)^n \\\\ & =1+\frac{1}{2}+\frac{1}{4} \ldots \ldots \ldots . \infty \\\\ & =\frac{1}{1-\frac{1}{2}} \\\\ & =2\lt\infty\\ \end{aligned}\\ $$

Hence the system is stable.